Topic 7A - Genetics Flashcards

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1
Q

Define these key words:

  1. Gene
  2. Allele
  3. Genotype
  4. Phenotype
A
  1. Gene = a sequence of DNA bases that codes for a particular protein.
  2. Allele = a different version of a gene
  3. Genotype =the combination of alleles (Bb)
  4. Phenotype =the organisms characteristics.
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2
Q

Define these key words:

  1. Dominant
  2. Recessive
  3. Codominant
  4. Locus
  5. Homozygote
  6. Heterozygous
  7. Carrier
A
  1. Dominant: allele whose characteristic appears in phenotype even if there’s only copy.
  2. Recessive: allele that needs to 2 copies to appear in phenotype
  3. Codominant: alleles that are both expressed in phenotype
  4. Locus: the fixed position of a gene on a chromosome. Alleles of a gene are found at the same locus on each chromosome in homologous pair.
  5. Homozygote: 2 copies of same allele
  6. Heterozygote: 2 copies of different allele.
  7. Carrier: A person carrying an allele which is not expressed in their phenotype but can be passed on to offspring
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3
Q

practise drawing monohybrid crosses

A

page 168

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4
Q

practise drawing Punnett square diagrams

A

page 169

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5
Q

How many alleles are there for each gene in a diploid organism?

A

2

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6
Q

How many alleles are there for each gene in gametes?

A

1

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7
Q

Define monohybrid inheritance

A

The inheritance of a characteristic controlled by a single gene

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8
Q

practise drawing codominance genetic diagrams

A

page 169

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9
Q

practise drawing blood group genetic diagrams

A

page 169

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10
Q

practise drawing dihybrid crosses

A

page 170

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11
Q

Define phenotypic ratio

A

The ratio of different phenotypes in offspring

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12
Q

What do dihybrid crosses show you?

A

They show you how 2 different genes are inherited at the same time

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13
Q

What are the main differences between the Y chromosome and the X chromosome?

A

The Y chromosome is smaller than the X chromosomes and carries fewer genes

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14
Q

Why are males more likely to inherit a sex-linked disorder such as colour blindness?

A
  • As the X chromosome is bigger, it carries more genes and therefore, determines more characteristics.
  • Some genes that are carried by the X chromosome have faulty alleles such as the one for colour blindness.
  • As females are XX, they need two copies of the faulty allele to show the characteristic, whilst males only need 1 as the Y chromosome doesn’t carry the faulty allele.
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15
Q

Practise drawing genetic diagrams for sex-linked disease

A

Page 171

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16
Q

Define:

  1. Autosome

2. Autosomal genes

A
  1. Autosome = Any chromosome that isn’t a sex chromosome

2. Autosomal genes = the genes found on the autosome

17
Q

What is important about genes found on the same autosome?

A

Genes on same autosome are said to be linked as it’s assumed they stay together during independent segregation of chromosomes in meiosis I, and their alleles will be passed on to offspring together. Only time this wont happen is if crossing over splits them up first
- The closer together 2 genes are on autosome, the more closely they are said to be linked. This is because crossing over is less likely to split them up

18
Q

How can autosomally linked genes affect the phenotypic ratio?

A

The result would most likely be that which you’d expect in a monohybrid cross, not a dihybrid cross, as the 2 autosomally-linked alleles are inherited together. This means a higher proportion of the offspring will have their parents genotype and phenotype.**

19
Q

practise drawing and explaining genetic diagrams that show autosomal linkage

A

page 172

20
Q

Does only one single gene control a characteristic?

A

No, many different genes can interact to control the same characteristic

21
Q

What is epistasis?

A

Epistasis is when an allele from 1 gene blocks the expression of the alleles of other genes (when they interact to control a phenotype)

22
Q

What do epistatic genes affect (in terms of expected phenotype ratios)?

A

Crosses involving epistatic genes don’t result in the expected phenotypic ratios as there is no chance a characteristic will be expressed if it is blocked by an epistatic gene.

23
Q

Practise questions on how to predict phenotypes of epistatic genes

A

page 173

24
Q

Practise questions on chi-squared

A

pages 174-175