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GMC > Mendelian genetics pt2 > Flashcards

Mendelian genetics pt2 Flashcards

1
Q

How many chromosomes do we have?

A

46

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2
Q

How are our chromosomes arranged?

A

23 homologous pairs
22 pairs of autosomes
& 1 pair of sex chromosomes

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3
Q

What is a Diploid cell?

A

Contains the diploid number of chromosomes:

2n = 46

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4
Q

What is a haploid cell?

A

Contains the haploid number of chromosomes:

n = 23

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5
Q

What is mitosis?

A

Process by which cells are replicated for growth, repair etc

Produces 2 daughter cells each diploid (2n)

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6
Q

What is meiosis?

A

Process by which gametes are produced

4 daughter cells each haploid (n)

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7
Q

What are the stages of meiosis?

A

Meiosis 1 –> REDUCTIONAL devision, homologous pairs are seperated reducing chromosomes no. by half

Meiosis 2 –> EQUATIONAL devision, sister chromatids are separated producing 4 haploid gametes

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8
Q

How is meiosis the origins of genetic variation?

A
  • Independent assortment
  • Crossing over
  • Humans have n=23, no. possible gametes 2^23
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9
Q

How does crossing over cause genetic variation?

A
  • Produces recombinant chromosomes that carry genes from 2 parents
  • Avg. 1-3 crossing over events per chromosome pair
  • Occurs in prophase 1
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10
Q

How does independent assortment cause genetic variation?

A

Chromosome placement not influenced by the placement of any of the others

Leads to an individual producing a colllection of gametes that differ from parents

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11
Q

How does random fertilisation allow for genetic variation?

A
  • Random nature of fertilisation = genetic variation
  • Fertilisation = 2^23 X 2^23 = 70 trillion diploid combinations
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12
Q

What does non-mendelian patterns of inheritance mean?

A

Not all traits follow this law:
- Genotypic ratios follow Mendel’s laws but phenotypes do not

  • Mendel’s laws do not apply
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13
Q

What is the degree of dominance?

A
  • In Mendel’s pea experiments the offspring always look like one of the parents
  • Mendel’s pea alleles show COMPLETE DOMINANCE
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14
Q

What is incomplete dominance?

(A non-Mendelian pattern of inheritance)

A
  • The pheotype of the heterozygote is intermediate between the phenotype of the dominant & recessive traits - blending of the traits
  • One trait is not really dominant over the other

e.g. human hair –> curly (homozygous) or straight (homozygous)

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15
Q

What are the non-mendilian patterns of inheritance?

A
  • Incomplete dominance
  • Codominance
  • Multiple alleles
  • Pleitrophy
  • Epistasis
  • Polyhenic inheritance
  • Environmental factors
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16
Q

What is codominance?

(Non-Mendilian patterns of inheritance)

A
  • When BOTH alleles for a trait are expressed in heterozygous offspring
  • Two dominant genes are expressed at the same time e.g. MN blood gap glycoproteins on the surface of RBCs
  • ABO also co-dominance but 3 alleles rather than 2
17
Q

What is multiple alleles?

(Non-Mendilian patterns of inheritance)

A
  • Most genes exist as more thna 2 alleles
  • e.g. ABO glood group
  • 4 phenotypes A B AB O
  • IA and IB are co-dominant - both carbohydrates present hwen they exist together in a genotype
18
Q

What is pleiotropy?

(Non-Mendilian patterns of inheritance)

A
  • Most genes are multiple phenotypic effects (plieotrophy) - not as simple as Mendel’s pea plants
  • Pleiotrophic alleles are responsible for the multiple symptoms associated w hereditary disease such as cystic fibrosis & sickle cell anaemia
19
Q

What is epistasis?

(Non-Mendilian patterns of inheritance)

A
  • Phenotypic expression of gene at one locus affets another gene as a different locus –> e.g. labrador coat
  • Black colour dominant to brown BB, Bb, bb= brown
  • Second gene determines whether pigment will be deposited in hair - dominant E results in deposition of either black or brown (BbEe) e=blonde
20
Q

What is polygenic inheritance?

(Non-Mendilian patterns of inheritance)

A
  • One character influenced by many genes
  • Generally quantitative traits - continuous variation
  • 2 or more genes on a single phenotype, e.g. height or skin colour (the shade you appear)
21
Q

What are environmental factors in genetic inheritance?

(Non-Mendilian patterns of inheritance)

A
  • In hydrangea flowers;
  • Same genetic variety can vary in colour depending on soil pH
22
Q

What are the instances where Mendel’s laws do not apply

A
  • Mitochondrial inheritance
  • Linkage
  • Linkage disequilibrium
23
Q

Why do Mendel’s laws not apply in Mitochondrial inheritance?

A

mtDNA is solely inherited through the maternal line

24
Q

Why do Mendel’s laws not apply with linkage?

A

Two genes that are close together phycially are linked - his laws can’t apply

25
Q

Why do Mendel’s laws not apply with linkage disequilibrium?

A

Because they are two alleles that are not inherited separately

GMC (6 decks)

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