18. Genetics and Inheritance

Question 1

Genotype

Answer 1

The genetic consitution of an organism

Question 2

Phenotype

Answer 2

The expression of a genotype and its interaction with the environment

Question 3

What is a gene

Answer 3

A sequence of bases on DNA that codes for one polypeptide

Question 4

What are alleles

Answer 4

Alternative forms of a gene

Question 5

What is a locus

Answer 5

The position of a gene on a chromosomes

Question 6

What is a dominant allele

Answer 6

Always expressed in the phenotype if its presentin the genotype

Question 7

Recessive allele

Answer 7

Only expressed in the phenotype if the dominant allele is absent

Question 8

Why is it important for an organism to have some characteristics that are catergoric when invesigating inheritence

Answer 8

So can clearly distinguish the characteristics tested - no intermediates
Characteristics will be genetically determined

Question 9

Why must an oranism reproduce sexually when investigating inheritence

Answer 9

So can see the effect or recombining alleles and get variation in the offspring

Question 10

Why is it important of an organisms to produce large numbers of offspring when investigating inheritence

Answer 10

-Will give representative data
-Large enough sample size
-Enough data for statistical analysis

Question 11

Why is it important for an organisms to have a short lifespan when investigating inheritance

Answer 11

Can obtain data quickly
Can observe several generations

Question 12

Why is it important for an organisms to be small when investigating inheritance

Answer 12

Easily kept
Reduces costs

Question 13

When is a monohybrid cross used

Answer 13

If inheritance of one gene coding for one characteristic, is studied

Question 14

Whats a testcross/ backcross

Answer 14

To determine which genotype an organism has by crossing it with an organism with a homozygous recessive phenotype
If any offspring are homozygous recessive then the unknown genotype is heterozygous

Question 15

If an offpring, from an unknown organisms during backcrossing, is dominant, why is the unkown genotype is only tentative

Answer 15

-random fertilisation of gametes, could just be heterozygous offspring by chance
-Large number of offspring

Question 16

What are codominant alleles

Answer 16

Those that are both expressed in the phenotype of a heterozygous organism
Gives rise to a third phenotype

Question 17

What is sex determination

Answer 17

Sex is determined by the combination of chromosomes in a cell / organism rather than the genes themselves

Question 18

What is sex linkage

Answer 18

Genes are carried on the sex chromosome and are inhertited in different ways in males and fremales

Question 19

What are the sdex chromosomes in males and femles

Answer 19

Males =X Y , Non-homologous
Female n = X X

Question 20

Why are males more likley to have the reccessive versions of the phenotype

Answer 20

Only one recessive allele needs to be present in order for it to be expressed
Women need 2

Question 21

What is the evidence for alleles being dominant / recessive in pedigree diagrams

Answer 21

-Look for where an offspring has a different phenotype to the parents

Question 22

What is evidence for sex-linkage in pedigree diagrams

Answer 22

-Look for much greater numbers of affected males than females, or no affected females at all

Question 23

What is evidence against sex-linkage in pedigree diagrams

Answer 23

-Look for where a female with recessive phenotypes has a son or father with the dominant phenotype

Question 24

What is a dihydbrid cross

Answer 24

Consideres have 2 different genes are inherited
Organisms will have 4 alleles in their genotype and the gametes produced by each individual will jhave 2 alleles

Question 25

What is epistasis

Answer 25

arises in a dihybrid cross when there is some form of interaction between the 2 genes, One is said to be epistatic over the other

Question 26

What is the common dihybrid ratio

Answer 26

9;3;3;1

Question 27

When are dashes used in genotypes

Answer 27

To show that either allele of a gene could give the same phenotype

Question 28

What is autosomal linkage

Answer 28

All the non-sex chromosomes
They vary in the number of genes they carry
2 genes on the same chromosome

Question 29

Why are genes on the same chromosomes said to be linked

Answer 29

they will stay together during independent assortment of chromosomes in the first division of meiosis.
their alleles will be passed on to the offspring together so fewer types of gametes will form. In a dihybrid cross this can result in unexpected offspring ratios.

Question 30

How likley is crossing over to occur

Answer 30

The closer together the genes are on the chromosomes, the less likely it is that crossing over will result in these recombinant genotypes.
A smaller proportion of recombinant genotypes indicates that the genes are closer together.