3.3.6 Inheritance Flashcards Preview

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Flashcards in 3.3.6 Inheritance Deck (54)
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1

Define gene

A sequence of bases on a DNA molecule that codes for a protein (polypeptide), which results in a characteristic

2

Define Genotype

The genetic constitution of an organism

(i.e. the alleles an organism has)

3

Define Phenotype

The expression of the genetic constitution and its interaction with the environment

(i.e. an organism’s characteristics)

4

Define Allele

A different version of a gene

5

Explain what is meant by a recessive allele

Only expressed in phenotype when 2 alleles are present

6

Explain what is meant by a dominant allele

Is always expressed in the phenotype

7

Explain what is meant by co-dominant alleles

Both alleles are expressed in the phenotype

8

Define Homozygous

An organism that carries 2 copies of the same allele

9

Define Heterozygous

An organism that carriers 2 different alleles

10

Define Carrier 

Person carrying an allele which isn't expressed in phenotype but can be passed on to offspring

11

Define Locus

Fixed position of gene on a chromosome

(Alleles of gene are found at same locus on each chromosome in a pair)

12

Define Autosome 

Any chromosome that is not a sex chromosome

13

Define Allosome 

Sex chromosome

14

What is monohybrid inheritance?

Inheritance of a characteristic controlled by a single gene

15

Draw a monohybrid cross showing how wing length is inherited in fruit flies when the parent's genotypes are NN x nn. Include the phenotypes and phenotypic ratio.

N - normal wings allele

n - vestigial (little) wings allele

16

Draw genetic diagram when the paren'ts genotypes are HNHS x HNHS (i.e. crossing 2 parents with sickle-cell trait (heterozygous))

HN = normal haemoglobin 

HS = sickle haemoglobin

17

In the ABO blood group system in humans there are 3 alleles for blood type: 

  • IO is the allele for blood group O 
  • IA is the allele for blood group A
  • IB is the allele for blood group B

Allele IO is recessive. Alleles IA and IB are codominant - people with genotype IAIB will have blood group AB.

Draw a genetic diagram that shows a cross between a heterozygous person with blood group A and a heterozygous person with blood group B.

18

What do dihybrid crosses show?

Show how 2 genes are inherited are once

19

Draw a dihybrid cross diagram for when the both parents' gentotype is RrYy. Include the phenotype and the phenotypic ratio.

  • R - round seed
  • r - wrinkled seed
  • Y - yellow seed
  • y - green seed 

20

21

When are characteristics said to be sex-linked?

When the allele that codes for a characteristic is located on a sex chromosome

22

Most genes on sex chromosomes are only carried on ___ chromosomes

X

(X-linked genes)

23

Explain why males are more likely than females to show recessive phenotypes for genes that are sex-linked

  • Males only have 1 X = 1 allele for sex-linked genes
  • ∵ have only 1 copy, express characteristic of allele even if its recessive

24

Colour blindness is a sex-linked disorder caused by a faulty allele carried on the X chromosome 

Given that the female parent is a carrier and the male is unaffected, draw monohybrid diagram (n = faulty allele for a colour vision)

25

What are autosomal genes?

Genes located on the autosomes

26

Genes on the same autosome are said to be ____

linked

27

Why are autosomal genes said to be linked?

  • ∵ they're on the same autosome, they'll stay together in independent segregation of chromosomes in meiosis I
  • And their alleles will be passed on to offspring together

(Only doesn't occur if crossing over splits them up 1st)

28

The closer together 2 genes are on autosome, the more ...

closely they're linked

29

Why is that the more closer together 2 genes are on autosome, the more closely they're linked?

∵ reduces the chance of genes being separated during crossing over

30

What happens to the phenotypic ratio expected in offspring when 2 gene are autosomally linked?

  • It changes - won't get the phenotypic ratio you expect in offspring of cross
    • e.g. Dihybrid cross between 2 heterozygous parents = 9:3:3:1 ratio in offspring
    • Instead phenotypic ratio more likely to be like monohybrid cross between heterozygous parents (3:1)

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