D3.2 Inheritance Flashcards

Question

What is Phenylketonuria (PKU)

Answer 1

PKU is caused by mutations in the PAH gene on an autosome (non sex chromosome; n=22). This gene normally codes for the enzyme phenylalanine hydroxylase which converts the amino acid phenylalanine to tyrosine. Without this enzyme, phenylalanine builds up to toxic levels, damaging the brain and nervous system. People with PKU must follow a low-protein diet to prevent toxicity (avoiding foods like eggs, meat, and nuts). They often take dietary supplements to replace nutrients missing from these food. PKU is an autosomal recessive disorder, meaning it occurs only in homozygous recessive individuals

Answer 2

it occurs only in homozygous recessive autosomes.

Answer 3

Albinism: caused by mutations in melanin producing genes, it results in lack of pigment in skin, hair, and eyes. Cystic fibrosis: mutation in CFTR gene, results in thick mucus in lungs and digestive tract. Sickle cell anemia: Mutation in hemoglobin gene (HBB), it results in RBCs to become sickle shaped. Tay-Sachs disease: mutation in HEXA gene, results in fatty buildup in brain cells, fatal in early childhood.

Answer 4

Recessive alleles often have loss-of-function mutations, meaning the protein they make doesn't work properly or isn't made at all. The dominant allele still makes enough normal protein to carry out the job. Since one functional copy is enough, the recessive trait is hidden. Sometimes the amount of protein matters (called a dosage effect). Example: Incomplete dominance → one copy of a working allele isn’t enough, so the trait is intermediate (like pink flowers). Other times, the type of protein changes the result: Codominance: both alleles make different functional proteins that are both expressed (e.g. A and B blood group proteins). In simple words, recessive alleles are usually caused by a loss of function mutation (protein doesn't work properly or isn't made at all), while dominant alleles are often the normal, fully functional version of the gene. However, dominant allele can also be a mutant that still makes a functional or over active (gain of function mutations; ex. Huntington's)

Answer 5

If the trait needs 50 units of protein for the normal function: AA might make 100 units Aa might make 60 units Both exceed 50, so they look the same. That’s why heterozygotes and homozygous dominants often have indistinguishable phenotypes. In some genes, having one copy doesn’t produce quite enough protein for the full effect. This is where incomplete dominance or codominance happens. Example: Flower color Red allele (R) → makes pigment White allele (r) → no pigment RR = lots of pigment → red Rr = medium pigment → pink rr = none → white In some, being homozygous dominant can enhance the trait or even cause problems through over expression toxicity.

Answer 6

SNP (Single Nucleotide Polymorphism): A single base change in DNA at a specific position. If it occurs in a gene, it can change the amino acid and produce a different allele. Multiple alleles: When a single gene has three or more alternative forms in a population. Ex. ABO blood group system

Answer 7

Gene: I Alleles: IA, IB, i IA makes A antigens (blood type A) IB makes B antigens (blood type B) I produces no antigens (blood type O) Genotype: IAIA or IAi = Type A IBIB or IBi = Type B IAIB = Type AB (codominant) ii = Type O (homozygous recessive)

Answer 8

Four o'clock flower Flower color gene: C with superscripts for allele C^R = red, C^W = white C^R C^W heterozygote = pink flowers (blend of red and white). Unlike codominance, the traits blend rather than appear separately.

Answer 9

Humans: XX = f, XY = M X chromosome = 800 genes, Y = 70 genes

Answer 10

Males produce sperm carrying either X or Y, giving a 50% chance of male or female offspring. Embryos intially develop similarly; sex hormones huid gonad differentiation: XX w high oest & prog leading to the development of ovaries, and XY w high test leading to testesssss. Y chromosome is much shorter. Very few genes on the Y are shared with the X.

Answer 11

traits that arise from expressions of genes located on X or Y chromosome (23rd chrom)

Answer 12

Haemophilia: a condition that affects the way your blood clots. XH=normal clotting XH= haemophilia Y= no allele. XHXH= female, normal XHXh= female carrier (normal) XhXh = female affected XHY = male normal XhY= male affected. Males cannot be carriers of X linked traits because they have only one X

Answer 13

Males have only one X and one Y. If the gene on their single X chromosome has a mutation, they don't have another copy to mask it because the Y doesn't carry that gene. So even if its recessive, it shows up in their phenotype, Ex: X^H Y = normal (blood clots properly) X ^ h Y = has hemophilia (no working clotting gene) females have two X chromosomes. If one X has the recessive mutation (X^h), the other normal X (X^H) can mask it. This is why females can be carriers, where they carry the allele but don't show the phenotype. X^H X^H = normal X^H X^h = carrier (normal phenotype) X^h X^h = affected

Answer 14

Polygenic inheritance happens when two or more genes (often on different chromosomes) combine to influence one trait. Since multiple genes are involved, there are many possible genotype combinations which leads to a wide range of phenotypes rather than just a few categories.

Answer 15

Human skin color (controlled by several pigment related genes) Height Body shape Intelligence or aptitude These traits don't fall into yes/no categories, but rather form a gradient (they show continuous variation)

Answer 16

continuous: Many possible phenotypes between two extremes; traits influenced by multiple genes (and often the environment). Bell-shaped curve / histogram or box and whisker plots. Occurs in polygenic traits. The phenotypes form a smooth range — e.g., very short → average → very tall. Height, skin color Discontinuous variation: Distinct categories with no intermediates; controlled by one gene or very few. Bar chart Blood type, flower color

Answer 17

Q1 (Quartile 1): 25th percentile Q2 (Median): 50th percentile Q3 (Quartile 3): 75th percentile Interquartile Range (IQR): Q3 − Q1 → measures data spread Box: represents IQR Whiskers: show min and max (excluding outliers) Outliers: If a value is more than 1.5 × IQR above Q3 or below Q1, it’s considered an outlier and not included in the whiskers.

Answer 18

breeding experiment that examines the inheritance of two different traits at the same time. Ex: seed color (Y/y) Seed shape (R/r) In a cross b/w two heterozygotes (RrYy x RrYy) there are 16 possible genotype combinations in the F2 generation. Phenotypic ratio: 9: 3: 3: 1

Answer 19

Each organism carries two alleles for every gene, but only one allele goes into each gamete (egg or sperm). This happens because of seperation of homologous chromosomes during meiosis I. = each parent contributes one allele per gene to the offspring.

Answer 20

Alleles of different genes are passed to games independently of one another, meaning the inheritance of one trait doesn't affect another. This is true only when the genes are on different chromosomes or are far apart on the same chromosome.

Answer 21

Linked genes are genes that are close together and tend to be inherited together. explain further

Answer 22

9:3:3:1 phenotypic ratio observed in dihybrid cross. This ratio appears in the second fillal (F2) generation when two parents that are heterozygous for two different traits are crossed. or 1:1:1:1 mating a heterozygous ind w a homozygous recessive

Answer 23

Genes must be on seperate chromosomes or far apart on the same chromosome (less than 50% recombination) Traits must be autosomal (not sex linked) exceptions exist (linked genes) but they don't invalidate Mendel's laws, just refines the rules.

Answer 24

Two or more genes are located close together on the same chromosome. They are usually inherited together and form a linkage group. This applies to autosomes and sex chromosomes.

Answer 25

Crossing over can seperate linked genes during meiosis, creating recombinat gametes, but if genes are very close, recombination is rare.

Answer 26

They are chromosomes with a new combination of alleles due to crossing over. Recombinant organism shows a new phenotype not seen in either parent. In a bivalent during meiosis: 2 gametes are parental combinations(less diversity), and 2 gametes are recombinant combinations. This is because only one chromatid from each homoogous chromosomes typically participates in a crossover event.

Answer 27

Traits for body color (G =grey, g = black), wing lenght (L=long, l=short) are linked. Ex: parental genotypes: grey long wing heterozygote (G L/g l) x black short wing homozygote (g l/ g l) without crossing over: G always inherited with L crossing over produces recombinants (new combinations of traits not present in parents)

Answer 28

It is used to determine if observed genetic ratios match expected ratios from a punnett square. It helps decide if differences are due to random change or significant deviation. the formula is X^2 sigma of (O - E) ^2 / E, where O is observed frequency, E is expected frequency. Compare X^2 value to a critical value (from chi squared table) to see if the difference is statistically significant. practical example: gene databases ex: ABO blood type gene Search NCBI for ABO. Chromosome location: 9q34.2 = 8= chromosome 9 q = long arm (p = short arm) 34.2 = distance from centromere RefSeq = histobloodgroup ABO system transferase

Answer 29

a. genotype refers to the alleles an organism possesses; 1 mark b. phenotype refers to the observable traits or characteristics; 1 mark c. same phenotype can result from different genotypes; 1 mark d. environment can influence the expression of phenotype; 1 mark e. genotype determines potential traits; 1 mark f. phenotype is the result of gene expression; 1 mark g. genotype includes dominant and recessive alleles;

D3.2 Inheritance Flashcards

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