inheritance

Question 1

define a gene

Answer 1

A sequence of bases on a DNA molecule that codes for a protein (polypeptide), which results in a characteristic, e.g. a gene for eye colour

Question 2

what is an allele

Answer 2

Different versions of the same gene that code for variants of a characteristic. Represented by letters, e.g. B = brown eyes, b = blue eyes

Question 3

whats a genotype

Answer 3

An organism’s genetic makeup - its alleles, e.g. BB, Bb, or bb

Question 4

whats a phenotype

Answer 4

An organism’s physical characteristics as determined by its genotype and environment

Question 5

define dominant allele

Answer 5

An allele that is always expressed in the phenotype, even when only one copy is present in the genotype (shown with an uppercase letter)

Question 6

define a recessive allele

Answer 6

An allele that is only expressed when it is homozygous in the genotype (two copies are present), and is masked by a dominant allele (shown with a lowercase letter)

Question 7

define locus

Answer 7

A locus (plural: loci) is the specific position of a gene on a chromosome

Question 8

define homozygous

Answer 8

An organism with two identical alleles for a trait is homozygous

Question 9

define heterozygous

Answer 9

An organism with two different alleles for a trait is heterozygous

Question 10

what is monohybrid

Answer 10

• the transmission of one gene from parents to their offspring.
• single characteristic controlled by one gene with two possible alleles.

Question 11

what happens if you cross 1 homo dom parent with 1 homo rec parent

Answer 11

offspring will be heterozygous, inheriting a recessive allele from one parent and a dominant allele from the other.
-all express the dominant trait in their phenotype

Question 12

what happens to the ratio when you corss to hetero parents

Answer 12

3:1

Question 13

whats a dihybrid cross

Answer 13

simultaneous inheritance of two genes controlling separate characteristics.

Question 14

what can dihybrid crosses help find

Answer 14

• Determine whether genes are linked.
• Locate genes on specific chromosomes.
• Calculate expected phenotypic ratios in subsequent generations.

Question 15

what is the law of independent assortment

Answer 15

means that alleles for different genes segregate independently during gamete formation in meiosis, unless they are linked.

Question 16

what happens in a dihybrid cross when both parents are both hetero

Answer 16

9:3:3:1

Question 17

what are the reasons for deviations from expected ratios in dihybrid crosses?

Answer 17

1. Random fertilisation:
   - Gamete fusion is random
2. Linked genes are on the same chromosome so alleles are usually inherited together.
   However, crossing over during meiosis =change allele combinations by separating linked genes.

Question 18

what is codominance?

Answer 18

• two different alleles are equally expressed in an org’s phenotype. both alleles share equal dominance.

Question 19

what are multiple alleles?

Answer 19

• genes that exist in more than two allelic forms. but individs can only have two alleles of a specific gene at any one time.
  = inc phenotypic diversity among ppl in a pop

Question 20

whats an example of multiple alleles

Answer 20

blood groups

Question 21

in blood, which groups are dominant

Answer 21

IA and IB are codominant
IO recessive

Question 22

explain how fertilisation is random in dihybrid fertilisation

Answer 22

2 genes are on seperate chromosomes.
- as chromosomes arrange themselves at random on the equator during meiosis, any of the 2 alleles for ___ can combine with either of the 2 alleles for ___

Question 23

what does mendel observe

Answer 23

law of independent assortment: each member of a pair of alleles may combine randomly with either of another pair

Question 24

how many pairs of chromosomes do ppl have

Answer 24

23
- 22 pairs have homologous partners that r identical in appearance

Question 25

explain allele expression in males

Answer 25

only have one X chromosomes often have 1 allele for sex-linked genes. express characteristic of allele even if recessive.

Question 26

examples of sex linked diseases

Answer 26

haemophilia red-green colourblindness duchenne muscular dystrophywhy

Question 27

why is x linkage more common

Answer 27

x chromosome is bigger part of it doesnt have a **homologous section on the y** ch = only 1 allele of a gene will be present so always expressed

Question 28

what is autosomal linkage

Answer 28

2 genes that occur on the same chromosome. - all genes on a single ch = linkage group. 22 ch except sex ch called autosomes

Question 29

how does autosomal linkage occur

Answer 29

- when gametes produced by meiosis - multiple sections of homologous ch r **exchanged** in **recombination.** - if 2 genes located in close **proximity on same ch** they r more likely to be exchanged together and be transmitted to gamete together than be **segregated** - do not segregate in accordance to mendels law of independent assortment

Question 30

in autosomal linkage, why is the expected ratio 3:1?

Answer 30

2 autosomally linked alleles r inherited together = higher proportion of offspring will have their parents genotype and phenotype.

Question 31

how to remember autosomal linkage

Answer 31

big letter always w small letter - PL pl

Question 32

what is epistasis

Answer 32

when the allele of 1 gene affects or masks the expression of another phenotype. can be dominant or recessive