cycle 5

Question 1

1800s blending theory of inheritance

Answer 1

offspring have characteristics of both parents, so offspring must be a blend of the parents’ generation

Question 2

how was the blending theory disproved?

Answer 2

would gradually lose diversity due to this, blue-eyed children to brown-eyed parents disproved this

Question 3

how did mendel employ the scientific method?

Answer 3

careful experimentation with controlled crosses and qualitative analysis

Question 4

mendel’s steps to controlled crosses

Answer 4

1. cutting off the anther prevents the plant from self-pollinating
2. brushing the pollen of the purple plant on the stigma of the white plant is cross-pollination
3. the new seeds that grow from the resulting seeds reveal which trait was dominant and which was recessive

Question 5

why were pea plants chosen?

Answer 5

easy to grow, low generation time, distinct characteristics, easy to mate

Question 6

mendel’s conclusions

Answer 6

1. variation in traits is due to different alleles
2. alleles segregate randomly into gametes
3. organisms inherit 2 alleles for each trait
4. appearance of heterozygotes is determined by dominant traits (recessive alleles masked for many generations)

Question 7

principle of segregation

Answer 7

two alleles of a gene segregate from each other during gamete formation

Question 8

principle of independent assortment

Answer 8

during the segregation of alleles into gametes, alleles of different pairs assort independently

Question 9

mendel’s principles

Answer 9

segregation and independent assortment

Question 10

what causes different alleles?

Answer 10

due to mutations or SNPs, don’t have to occur at the same place, only on the same gene

Question 11

OCA2 gene and eye colour

Answer 11

• OCA2 allele 1: produces a lot of p-protein, allows melanosomes to produce a lot of melanin, brown eyes
• OCA2 allele 2: produces little p-protein, melanosomes produce little melanin, blue eyes

Question 12

monohybrid crosses

Answer 12

consider one trait and predict the distribution of offspring (distribution of genotypes ≠ distribution of phenotypes)

Question 13

dihybrid crosses

Answer 13

alleles of 2 genes assort independently (2 different traits are inherited independently of each other if coded on different genes)

Question 14

incomplete dominance

Answer 14

when an individual is heterozygous with incompletely dominant alleles, the phenotypic expression is a mix of both traits- intermediate expression (pink plants who have 1 red and 1 white allele)

Question 15

Tay Sachs (prevents the production of lysosomal enzymes- HEX-A)

Answer 15

example of incomplete dominance

• no Tay Sachs: lots of HEX-A protein to break down fats
• mild Tay Sachs: heterozygous- produces enough HEX-A to live normally
• severe Tay Sachs: no HEX-A, fatty structures accumulate in nerve cells and nerves are deteriorated

Question 16

codominance

Answer 16

codominant alleles are equally expressed in heterozygotes

Question 17

blood types

Answer 17

example of codominance
-type A: IAIA or IAi
-type B: IBIB or IBi
-type AB: IAIB
-type O: ii
alleles are the code for enzymes to attach sugar units (antigens) to the surface of RBCs

Question 18

glycoproteins and ABO blood types

Answer 18

on RBC membranes, ABO antigens differ only by the terminal sugar group attached to the protein (by glycosyltransferase)

• gene on type A, B, AB is functional and codes for enzymes ability to add sugars (type AB codes for 2 types of enzymes)
• type O has a mutated allele and creates a non-functional protein that can’t attach a terminal sugar (no antigens)

Question 19

XX vs XY chromosomes

Answer 19

XX are homologous, XY are not

Question 20

X-linked inheritance (recessive)

Answer 20

males need only one affected X to display disorder, females need both affected X to display disorder (females with one affected X and one normal- carrier)

Question 21

red-green colour blindness

Answer 21

x-linked recessive

Question 22

polygenic traits

Answer 22

determined by the collective influence of multiple genes/alleles (intermediate phenotype is the most common)

Question 23

epistasis

Answer 23

a form of non-Mendelian inheritance in which one gene is capable of interfering with the expression of another
(e.g. one gene codes for the production of pigment, another one codes for the deposition of the pigment)

Question 24

the equation for the number of different genotypes

Answer 24

2^n (n is the number of heterozygous pairs in the genotype)