Section 7 - Chapter 17: Inherited Change - old Flashcards

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1
Q

Why do we resemble our parents but are not identical?

A
  1. Inherit alleles/ genes from both parents. Fusion of gametes. Gametes are haploid.
  2. When egg/sperm meet we have 2 copies of each gene
  3. Some are dominant and recessive.
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2
Q

What is a gene?

A

Short section of DNA on a chromosome, this is a sequence of nucleotide bases that code for a specific protein.

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3
Q

What is an allele?

A

Different forms/versions of a gene

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4
Q

What is the genotype?

A

The genetic constitution of an organism. Combination of alleles. e.g Bb. Can be influenced by environment/mutations

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5
Q

What is the phenotype?

A

Observable or biochemical characteristics of an organism due to genotype/allele and the environment

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6
Q

What does homozygous mean?

A

Where 2 alleles for a given gene are the same ( BB)

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7
Q

What does heterozygous mean?

A

Where 2 alleles for a given gene are different (Bb)

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8
Q

What does dominant allele mean

A

A dominant allele is always expressed in the phenotype

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9
Q

What does recessive allele mean?

A

An allele that influences the phenotype if 2 copies are present

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10
Q

What is codominance?

A

When 2 alleles have equal influence in the phenotype.

Phenotype can be a blend of both alleles (colour) or both features are represented separately (Blood Group)

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11
Q

What did Mendel discover when he crossed tall and dwarf pea plants

A
  • The gene that controls height in pea plants has 2 alternative forms called alleles
  • The allele for tallness is dominant and allele for shortness is recessive.
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12
Q

What are dihybrid crosses used

A

Shows how 2 characters determined by 2 different genes located on different chromosomes are inherited.

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13
Q

What are multiple alleles

A

Where there are more than 2 alleles of which only 2 may be present at the loci of an individual’s homologous chromosomes

e.g blood group

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14
Q

How many pairs of chromosomes do humans have

A

23 pairs

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15
Q

What is the 23rd pair also known as and what are they for male and female

A
  • 23rd pair is the sex determining chromosomes
  • XX is female and XY is male
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16
Q

Any gene that is carried on either X or Y chromosome is said to be …. and which is longer

A
  • Sex-linked
  • The X chromosome is longer and for most of the chromosome there is no equivalent homologous portion to match with the Y chromosome.
17
Q

What is haemophilia

A
  • Defective gene on the x chromosome
  • Blood clots slowly and internal bleeding
  • Affected individuals have a mutated allele (recessive) which results in a non-functional protein
18
Q

Exam Question : Male fruit flies are more likely to show a phenotype produced by a recessive allele carried on the X chromosome. Explain why

A

As males have only 1 X chromosome they only need 1 recessive allele to show the phenotype however females must present 2 recessive alleles as they have 2 X chromosomes.

19
Q

Exam Question: During meiosis, when the X and Y chromosome pair up they dont form a typical bivalent. Explain why

A

X and Y chromosomes are different sizes so chromatids are unable to line up and form bivalent/ only short pairing region/ most of length not homologous.

20
Q

Couple 1 and 2 have the disorder and have 3 children in which 1 doesn’t have the disorder. How can you tell the disorder is caused by a dominant allele.

A

The couple have a son that doesnt have the disorder whilst they do.

They therefore must be heterozygous and as they have the disorder it must be dominant.

21
Q

Couple 3 and 4 dont have the disorder but their daughter does. How can you tell the condition is caused by a recessive allele.

A

3 and 4 dont have the disorder but their daughter does therefore they must be carriers and passed on their recessive alleles.

22
Q

In fruit flies, the genes for body colour and wing length are linked. Explain what this means

A

The genes are on the same chromosome

23
Q

What are the remaining 22 chromosomes (not sex determining) called and what is the name when genes are located on the same autosome.

A
  • Autosomes. The name given to the situation where 2 or more genes are carried on the same autosome is called autosomal linkange
24
Q
A
25
Q

Why are the ratios of 2 phenotypes more than others in autosomal linkage

A
  • Linked genes remain together during meiosis and therefore remain together when they pass into the gamete.
  • Small numbers in other phenotypes are due to crossing over.
26
Q

Distinguish between sex-linkage and autosomal linkage

A
  • In sex linkage the linked genes are on the same sex chromosome whereas in autosomal linkage they are on any chromosome other than the sex chromosomes.
27
Q

What is epistasis and give an example

A
  • Epistasis arises when the allele of 1 gene affects or masks the expression of another in a phenotype. Coat colour in mice.
28
Q

What is a species

A

A group of similar organisms that can reproduce to produce fertile offspring

28
Q

What is a species

A

A group of similar organisms that can reproduce to produce fertile offspring

29
Q

What is a population

A

A group of organisms of the same species that occupies a particular area at the same time

30
Q

What is a Gene Pool

A

All the alleles of all the genes of all the individuals in a population

31
Q

What is Allele Frequency

A

Number of times a particular allele occurs within the gene pool (Usually given as a % or decimal)

32
Q

What is the Hardy Weinberg Principle

A
  1. Predicts the frequencies of alleles in a population won’t change from generation to generation
  2. Assumption that proportion of dominant and recessive alleles remain the same from generation. 5 conditions need to be met.
33
Q

What are the 5 conditions that mean Hardy Weinberg Principle can be used.

A
  1. There is no selection - all alleles are equally likely to be passed on
  2. No mutations take place
  3. There is a large population
  4. Mating within the population is random
  5. No emigration/ immigration - no alleles enter or leave the population
34
Q

What can the 2 Hardy Weinberg equations be used for

A
  1. Estimate the frequency of particular alleles
  2. Test whether or not the HW principle applies to particular alleles - to test whether other factors affect allele frequencies.
35
Q

What is the equation for allele frequency

A
  • p+q = 1, p= frequency of dominant allele. q = recessive allele.
  • The total frequency of all the possible alleles for a characteristic in a population is 1.0.
36
Q

What is the equation for genotype frequency

A
  • p2 + 2pq + q2 = 1 , p2 = frequency of homozygous dominant. 2pq = heterozygous, q2= homozygous recessive.
  • Total frequency of all possible genotypes. 3 genotypes.
    *