1
Q
What is meiosis?
A
The process of reductive cell division producing four haploid (n) gametes from a single diploid (2n) germ cell
Meiosis is essential for sexual reproduction and occurs only in germline cells that produce sperm and ovum.
2
Q
How many rounds of division does meiosis consist of?
A
- Meiosis I (reductional division)
- Meiosis II (equational division)
Meiosis I separates homologous pairs, while Meiosis II divides sister chromatids.
3
Q
During which phase of meiosis do homologous chromosomes pair together to form a tetrad?
A
Prophase I
A tetrad consists of 2 chromosomes and 4 chromatids.
4
Q
What is the significance of chiasmata during meiosis?
A
They hold tetrads together and allow for crossing over
Crossing over provides genetic variation for the next generation.
5
Q
What is the process called when whole chromosome segments are exchanged during meiosis?
A
Crossing over (also known as synapsis or recombination)
This process occurs during prophase I and helps increase genetic diversity.
6
Q
What forms when crossing over occurs between two chromosomes?
A
A synaptonemal complex
This complex is formed as nucleotides are exchanged between the paired chromosomes.
7
Q
What type of cells undergo meiosis?
A
Germline cells
These cells produce sperm and ovum necessary for sexual reproduction.
8
Q
What are the two types of chromatids involved in meiosis?
A
- Homologous chromosomes
- Sister chromatids
Homologous chromosomes pair during meiosis I, while sister chromatids are separated during meiosis II.
9
Q
What is the relationship between the proximity of genes on a chromosome and their likelihood of being linked?
A
The closer together two genes are located on a chromosome, the more likely they are to be linked
This means they are less likely to have a crossover occur between them during prophase 1.
10
Q
What does synapsis refer to in genetics?
A
Pairing of homologous chromosomes
This process occurs during prophase 1 of meiosis.
11
Q
During metaphase 1 of meiosis, homologous chromosomes are arranged as a __________.
A
tetrad
They move to the metaphasic plate where they arrange themselves randomly.
12
Q
What is the term for the random assortment of chromosomes during disjunction?
A
Independent assortment
This generates genetic variation in daughter cells.
13
Q
True or false: Linked genes are typically inherited together because they are located on the same chromosome.
A
TRUE
This is due to the low probability of crossing over occurring between them.
14
Q
What is the significance of independent assortment during meiosis?
A
It generates genetic variation
Each daughter cell receives a random assortment of chromosomes with mixed paternal and maternal origins.
15
Q
What is the result of meiosis 1 in terms of chromosome number?
A
Each daughter cell possesses a haploid genetic complement of 23 chromosomes/46 chromatids
This occurs after telophase 1 and cytokinesis.
16
Q
Name the three mechanisms that increase genetic diversity in sexually reproducing eukaryotes.
A
- Crossing over in prophase I of meiosis
- Random independent assortment in metaphase I of meiosis
- Fertilization of gametes
These mechanisms contribute to the genetic variation in offspring.
17
Q
After the completion of the second round of meiosis, how many haploid gametes are produced?
A
4 haploid gametes
This is the result of the meiotic process.
18
Q
Fill in the blank: Two gametes must come together during _______ to produce a new diploid cell.
A
fertilization
This process is essential for sexual reproduction.
19
Q
What does crossing over in prophase I of meiosis contribute to?
A
Increased genetic diversity
This process allows for the exchange of genetic material between homologous chromosomes.
20
Q
What is the significance of independent assortment in metaphase I of meiosis?
A
It contributes to genetic diversity
This mechanism ensures that alleles segregate independently during gamete formation.
21
Q
What is a gamete?
A
A reproductive cell that carries half the genetic information
Gametes are produced through meiosis.
22
Q
True or false: Each parent can produce 8 different gametes if they have 3 genes with 2 options each.
A
TRUE
The number of gametes can be calculated as 2^n, where n is the number of genes.
23
Q
What is nondisjunction in meiosis?
A
Failure of chromosome pairs to separate at anaphase I or sister chromatids to separate in anaphase II
This error results in a cell with an imbalance of chromosomes, known as aneuploidy.
24
Q
What is monosomy?
A
Loss of a single chromosome in the zygote (2n - 1)
Most monosomies in humans are not viable; the only survivable monosomy is Turner syndrome (45 chromosomes).
25
What is **trisomy**?
Addition of a single chromosome in the zygote (2n + 1)
## Footnote
Survivable trisomies include sex chromosome trisomies (XXX, XXY, XYY) and three autosomal trisomies (Patau syndrome, Edward's syndrome, Down's syndrome).
26
What is the only survivable monosomy in humans?
Turner syndrome (single X sex chromosome)
## Footnote
Turner syndrome is characterized by having a total of 45 chromosomes.
27
What are the common examples of **trisomy** in humans?
* Patau syndrome (chromosome 13)
* Edward's syndrome (chromosome 18)
* Down's syndrome (chromosome 21)
## Footnote
These are the only survivable autosomal trisomies.
28
What is the frequency of **sex chromosome aneuploidy**?
Around 1 in 1000 births
## Footnote
This includes conditions like Turner syndrome and Klinefelter's syndrome.
29
What is **Klinefelter's syndrome**?
Trisomy of the sex chromosomes (XXY)
## Footnote
Individuals with Klinefelter's syndrome have a total of 47 chromosomes.
30
True or false: Nondisjunction can occur during **mitosis**.
TRUE
## Footnote
While nondisjunction in mitosis usually has minimal impact, it can be severe during embryogenesis.
31
What happens to gametes during **nondisjunction in meiosis I**?
½ gametes affected
## Footnote
This leads to an imbalance in chromosome number in the resulting gametes.
32
What happens to gametes during **nondisjunction in meiosis II**?
Some gametes affected
## Footnote
This results in a mix of normal and aneuploid gametes.
33
What is the **purpose** of **mitosis**?
Asexual replication
## Footnote
Mitosis results in the production of somatic cells.
34
What is the **purpose** of **meiosis**?
Sexual reproduction
## Footnote
Meiosis produces gametes (eggs and sperm).
35
How many **cell divisions** occur in **mitosis**?
1
## Footnote
This results in 2 diploid cells.
36
How many **cell divisions** occur in **meiosis**?
2
## Footnote
This results in 4 haploid cells.
37
What is the **daughter ploidy** of cells produced by **mitosis**?
Diploid, genetically identical to parent
## Footnote
Mitosis produces two diploid daughter cells.
38
What is the **daughter ploidy** of cells produced by **meiosis**?
Haploid, genetically different from parent
## Footnote
Meiosis produces four haploid daughter cells.
39
During **anaphase I** of meiosis, what happens to **homologous chromosomes**?
Moved to separate sides of the cell
## Footnote
This is a key step in the reduction of chromosome number.
40
During **anaphase II** of meiosis, what happens to **sister chromatids**?
Pulled apart
## Footnote
This leads to the formation of haploid cells.
41
What are the **offspring genotypes** if the mother cat has **blue eyes** (recessive allele) and the father cat has **brown eyes** (heterozygous)?
* Bb (brown eyes)
* bb (blue eyes)
## Footnote
The offspring can inherit either allele from each parent.
42
What is **nondisjunction**?
Error in chromosome separation during meiosis
## Footnote
This can lead to aneuploidy in offspring.
43
In the context of meiosis, where could an **error** have occurred in a **G2 cell**?
During chromosome replication or separation
## Footnote
Errors in G2 can affect the outcome of meiosis.
44
What is **codominance**?
A genetic scenario where both alleles in a heterozygote are fully expressed
## Footnote
This results in a phenotype that is neither dominant nor recessive.
45
Define **Mendelian genetics**.
A set of primary tenets relating to the transmission of hereditary characteristics from parent organisms to their offspring
## Footnote
It includes concepts such as segregation and independent assortment.
46
What are **chromosomes**?
Structural units of genetic material consisting of a double-stranded DNA molecule and its associated proteins
## Footnote
Genes are located on chromosomes.
47
What is a **locus**?
The position of a gene along a chromosome
## Footnote
It is where alleles are found.
48
What are **alleles**?
Versions of a specific gene
## Footnote
They can be dominant or recessive.
49
What does **homozygous** mean?
Having two identical alleles for a specific gene
## Footnote
Example: AA or aa.
50
What does **heterozygous** mean?
Having two different alleles for a specific gene
## Footnote
Example: Aa.
51
What is the difference between **genotype** and **phenotype**?
* Genotype: Actual genes (homozygous or heterozygous)
* Phenotype: Physical/physiological expression of those genes
## Footnote
Example: Genotype Aa may express as a tall plant (phenotype).
52
What are the **possible genotypes** for a gene with two alleles?
* AA
* Aa
* aa
## Footnote
These represent homozygous dominant, heterozygous, and homozygous recessive respectively.
53
What are the **possible phenotypes** for a gene with two alleles?
* Dominant phenotype
* Recessive phenotype
## Footnote
Example: Purple (dominant) and white (recessive) flowers.
54
What did **Gregor Mendel** demonstrate with his pea plant experiments?
His two major laws of inheritance: Segregation and Independent Assortment
## Footnote
These laws explain how traits are inherited.
55
What is a **monohybrid cross**?
A genetic cross between parents differing in a single trait
## Footnote
It helps determine the genotypic and phenotypic ratios of progeny.
56
What is the **Punnett square** used for?
To predict the genotypic and phenotypic ratios of offspring from a genetic cross
## Footnote
It visually represents the combinations of alleles.
57
In a monohybrid cross of purple (A) and white (a) flowers, what is the **F1 generation** ratio?
100% heterozygotes (Aa)
## Footnote
All offspring will express the dominant phenotype.
58
What is the **F2 generation** ratio in a monohybrid cross?
3:1 ratio of dominant to recessive phenotypes
## Footnote
Example: 3 purple flowers to 1 white flower.
59
What is a **Test Cross** (Back Cross) used for?
To determine if an individual exhibiting a dominant trait is homozygous or heterozygous for that trait
## Footnote
This method involves crossing the individual with a homozygous recessive.
60
In a Test Cross, what must you cross the individual with?
A homozygous recessive
## Footnote
This is essential to determine the genotype of the individual exhibiting the dominant trait.
61
If a plant with a dominant phenotype (purple) is crossed with a homozygous recessive (white), what are the possible genotypes of the dominant plant?
* Homozygous (AA)
* Heterozygous (Aa)
## Footnote
The test cross helps to identify which genotype the dominant phenotype possesses.
62
What are the two possible types of crosses in a Test Cross involving a purple flower?
* aa x Aa
* aa x AA
## Footnote
These crosses help to determine the genotype of the purple flower.
63
What is the outcome of a cross between aa and Aa?
* Half are purple
* Half are white
## Footnote
This occurs due to the inheritance of the dominant or recessive allele from the unknown genotype.
64
What is the outcome of a cross between aa and AA?
All are purple
## Footnote
This is because all offspring inherit the dominant allele from the homozygous dominant parent.
65
What is a **dihybrid cross** used for?
To look at the inheritance pattern of two separate characteristics
## Footnote
Mendel's laws of Independent Segregation and Independent Assortment were derived using dihybrid crosses.
66
In a dihybrid cross, what is assumed about the parents?
They are heterozygous crossed to heterozygous
## Footnote
*di* = two; *hybrid* = from two different homozygous parents.
67
What are the dominant and recessive traits for peas in the example provided?
* Round (dominant R)
* Wrinkled (recessive r)
* Yellow (dominant Y)
* Green (recessive y)
## Footnote
The example illustrates the inheritance of these traits in pea plants.
68
What is the expected phenotypic ratio from a dihybrid cross of two independent genes?
9:3:3:1
## Footnote
This ratio is observed if the traits are inherited with normal Mendelian genetics (dominant/recessive).
69
What can alter the expected 9:3:3:1 ratio in a dihybrid cross?
Gene interaction (epistasis)
## Footnote
This can lead to ratios such as 12:3:1, 9:3:4, or 9:7.
70
In the example, what is the chance of obtaining a **dominant phenotype**?
3/4
## Footnote
This represents the probability of offspring exhibiting the dominant traits.
71
In the example, what is the chance of obtaining a **recessive phenotype**?
1/4
## Footnote
This represents the probability of offspring exhibiting the recessive traits.
72
What are the possible offspring phenotypes from the cross of RRYY and rryy?
* Yellow round
* Green round
* Yellow wrinkled
* Green wrinkled
## Footnote
These phenotypes result from the combinations of dominant and recessive traits.
73
What is the **genotype** of the F1 generation in the example?
RrYy
## Footnote
This genotype results from the cross of heterozygous parents.
74
What is the **actual ratio** of phenotypes observed in the example?
9/16 Yellow round, 3/16 Green round, 3/16 Yellow wrinkled, 1/16 Green wrinkled
## Footnote
This supports the hypothesis of Mendelian inheritance.
75
In a **dihybrid test cross**, what ratio is observed when a heterozygous Fz progeny is test crossed with a homozygous recessive individual?
1:1:1:1
## Footnote
This ratio confirms the presence of a heterozygous genotype in the Fa progeny of the original dihybrid cross.
76
What are the **genotypes** involved in the dihybrid test cross example?
* SsBb
* ssbb
## Footnote
These genotypes represent the heterozygous and homozygous recessive individuals in the test cross.
77
In maize, what is the dominant allele necessary for **seed colour**?
A
## Footnote
The recessive allele for seed colour is represented by 'a', which results in colourless seeds.
78
What is the recessive allele in maize that results in **waxy starch**?
wx
## Footnote
The normal starch is represented by the dominant allele 'Wx'.
79
What is the expected Mendelian frequency of phenotype for offspring when a plant of genetic constitution **AaWxWx** is test-crossed?
* Half will be coloured, half will be colourless
* All will have normal starch
## Footnote
The test cross results in a segregation of traits due to independent assortment during meiosis.
80
True or false: In a dihybrid test cross, the two genes segregate independently during **meiosis**.
TRUE
## Footnote
This independent segregation is a key principle of Mendelian genetics.
81
What is an **allele**?
Code for isseryme
## Footnote
Alleles are variants of a gene that determine specific traits.
82
Define **co-dominance**.
Heterozygote fully expresses the phenotype of both alleles
## Footnote
Blood types A and B alleles are classic examples.
83
What occurs in **incomplete dominance**?
Dominant allele does not completely mask recessive allele
## Footnote
Heterozygous individual shows an intermediate phenotype.
84
What is the **P-Generation**?
Parents with homozygous genotypes
## Footnote
They contribute alleles to the offspring.
85
What does the **F1-Generation** represent?
Offspring from the P-Generation
## Footnote
Typically shows heterozygous phenotypes.
86
What is the **Law of Segregation**?
Alleles segregate during gamete formation
## Footnote
Illustrated by Punnett squares.
87
What is a **Mendelian trait**?
Controlled by a single locus with simple inheritance pattern
## Footnote
Follows Mendelian ratios.
88
Define **non-Mendelian inheritance**.
Inheritance patterns where traits do not follow Mendelian laws
## Footnote
Includes genomic imprinting, mosaicism, gene conversion, etc.
89
What is the phenotype of a **heterozygous** individual in co-dominance?
Expresses both phenotypes
## Footnote
Example: Blood type AB expresses both A and B antigens.
90
In incomplete dominance, the phenotype is a blend of which two types?
* Homozygous dominant
* Homozygous recessive
## Footnote
This results in an intermediate phenotype.
91
What is **penetrance** in genetics?
The probability of a gene or allele being expressed if it is present
## Footnote
Incomplete penetrance means a dominant allele is not always expressed in heterozygous individuals.
92
Define **expressivity** in genetics.
The degree to which a phenotype is expressed by individuals with the same genotype
## Footnote
For example, the severity of a disease can differ between two people with the same disease genotype.
93
What is the expected Mendelian ratio for a cross between a homozygous recessive white flower (rr) and a homozygous dominant red flower (RR)?
1 red flower, 1 pink flower
## Footnote
This represents the F1 generation where incomplete dominance occurs.
94
If two F1 generation flowers are crossed, what is the expected ratio for the F2 generation flowers?
1 red flower, 2 pink flowers, 1 white flower
## Footnote
This follows the Mendelian ratio for incomplete dominance.
95
True or false: In **complete dominance**, the penetrance of the dominant allele is 100%.
TRUE
## Footnote
The recessive allele has a penetrance of 0% in complete dominance.
96
What are the two types of penetrance mentioned?
* Complete penetrance
* Incomplete penetrance
## Footnote
Complete penetrance means the dominant allele is always expressed, while incomplete means it is not.
97
Fill in the blank: Individuals with the same genotype can differ in phenotype due to _______.
penetrance, expressivity or other non-Mendelian inheritance patterns
## Footnote
Normal Mendelian inheritance is characterized by simple dominant/recessive traits.
98
What is the expected outcome when a homozygous recessive white flower is crossed with a single flower from the F1 generation?
4 F2 generation flowers
## Footnote
This is part of the experiment to observe Mendelian ratios.
99
What does **Mendel's Law of Segregation** state?
Alleles separate independently when forming gametes
## Footnote
A gamete receives only one allele during gamete formation, and a zygote receives two, one from each parent.
100
During which process does the **Law of Segregation** occur?
Meiosis I
## Footnote
This law describes the separation of homologous pairs.
101
What is the outcome of **Mendel's Law of Independent Assortment**?
Alleles of genes on different chromosomes assort independently during gamete formation
## Footnote
This occurs during metaphase I of meiosis.
102
In which phase of meiosis do homologous chromosomes align independently according to the **Law of Independent Assortment**?
Metaphase I
## Footnote
Different arrangements of homologous chromosomes lead to varied allele inheritance.
103
What is the result of independent assortment in terms of allele inheritance?
Different alleles are inherited from each gamete produced
## Footnote
This applies to sexually reproducing organisms.
104
If a parent is **WwBb**, what are the possible gametes produced due to independent assortment?
* WB
* Wb
* wB
* wb
## Footnote
All options are equally likely due to independent assortment.
105
What does **crossing over** provide in terms of genetic recombination?
Another level of genetic recombination beyond independent assortment
## Footnote
Crossing over occurs in prophase I before independent assortment takes place.
106
The likelihood that alleles will remain together during crossover is **indirectly proportional** to what?
The distance separating them
## Footnote
If genes are located on the same chromosome, their proximity affects their inheritance.
107
In **Scenario 1**, if A1/B1 and A2/B2 are close to each other on their respective homologous chromosomes, what is more likely to happen?
They will be inherited together
## Footnote
This scenario indicates linked genes.
108
In **Scenario 2**, if A1/B1 and A2/B2 are far away from each other on their respective homologous chromosomes, what is more likely to occur?
Independent assortment
## Footnote
This scenario indicates unlinked genes.
109
If locus (gene) A and locus (gene) B are **linked loci**, what gametes can occur?
A1B1 and A2B2
## Footnote
Only these combinations can occur if the genes are linked.
110
If locus (gene) A and locus (gene) B are **unlinked**, what is the possible combination of gametes?
* A1B1
* A2B2
* A1B2
* A2B1
## Footnote
These combinations occur in a 1:1:1:1 ratio.
111
In the example provided, what percentage represents the **crossover** for the gametes Ab and aB?
10%
## Footnote
This indicates the frequency of crossover events between linked genes.
112
What does it mean if genes A and Bo are described as **linked**?
They are together on the same chromosome
## Footnote
This affects the inheritance patterns of these genes.
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