Inheritance of simple and complex traits

Question 1

what did the first models of heredity proposed by Hippocrates say

Answer 1

proposed that each part of the body in a sexually mature adult produces a substance that collects in the reproductive organs that determine the inherited characteristics of the offspring

Question 2

what did Aristotle propose about heredity

Answer 2

that the process of heredity transmits only the potential for producing traits, or characteristics, present in parents and not the traits themselves

Question 3

what did Darwin propose as an early model of inheritance

Answer 3

predicted that ‘gemmules’ are partciles of inheritance passed down to offspring, predicted blending inhertiance.

Question 4

what is blending inheritance

Answer 4

when traits in the offspring resemble the average of those in the parents which suggest variation would be lost over time

Question 5

what are the problems with Darwins proposed theory of inhertance

Answer 5

• populations would become more homogenous over time
• rare beneficial traits would be lost

Question 6

what did Gregor Mendel do in 1856-64

Answer 6

hybridised different pea varieties and characterised seven traits which proved it is the genes not traits which are transmitted in inheritance

Question 7

what were the 7 traits focused on my mendel

Answer 7

colour, shape, colour of pods, shape of pods, colour of flower, position of flowers and plant height

Question 8

what is the addition rule for mendelian inheritance

Answer 8

when possibilities are mutually exclusive, add the probabilities
e.g. Aa x Aa probability of a single zygote is 1/4 +1/4 = 1/2

Question 9

what is the multiplication rule fo mendelian inheritance

Answer 9

when outcomes can occur simultaneously and the occurrence of one doesnt affect the other, multiply probabilities
e.g.
Aa x Aa, probability of two offspring both being aa is 1/4 x1/4 = 1/16

Question 10

what is independent assortment

Answer 10

gametes segregate without being affected by other alleles

Question 11

what happens if genes dont assort independently

Answer 11

they show linkage disequilibrium
e.g. if they are close on the same chromosome or if they are sex-linked

Question 12

what is incomplete dominance

Answer 12

phenotypes of the hertozygous genotype intermediate between those of the homozygous genotypes

Question 13

what is incomplete penetrance

Answer 13

the trait is not always expressed due to environmental effects or effects of other genes

Question 14

what is variable expressivity

Answer 14

the trait is always expressed but the severity varies

Question 15

what is Brachydactyly

Answer 15

a dominant trait in which the middle bone finger fails to grow

Question 16

what happens in a recessive trait pedigree

Answer 16

1) the trait skips one or more generations
2) females and males = likley to be affected
3) affected individuals often result from mating between relatives

Question 17

give an example of X-linked inheritance

Answer 17

hemophilia - results from recessive mutation in gene encoding protein needed for blood clots

Question 18

what is a quantitative trait

Answer 18

traits measured along a continuum and are very common, quantitative genetics tries to uncover the underpinnings of complex traits
- many genes can be involved

Question 19

give an example of a genome-wide association studies

Answer 19

genetic variants associated with critical illness in covid-19

Question 20

what can affect the expression of complex traits

Answer 20

lifestyle choices and other environmental factors e.g. less nutrition, a high junk-food diet is a risk factor for diabetes

Question 21

what is an inbred line

Answer 21

individuals of a particular species which are nearly identical to each other in genotype due to long inbreeding.

Question 22

define heritability

Answer 22

the proportion of variation in a trait due to genetic differences amoung individuals

Question 23

how can heritability be estimated

Answer 23

1) comparing parents and offsprings
2) Twin studies - fraternal vs identical

Question 24

what is concordance

Answer 24

the percentage of cases in which both members of a pair of twins show a trait (out of cases where at least one twin shows the trait)