Inheritance

Question 1

What is a gene?

Answer 1

A sequence of DNA bases (triplets) that codes for a specific primary polypeptide chain

Genes for particular traits are found in the same location on the chromosome (locus) in different individuals of the same species

You can get different mature mRNA from the same gene

Question 2

What are homologus chromosomes?

Answer 2

Same size, same locus, same gene

Question 3

What are alleles?

Answer 3

Alternative forms of genes occupying a similar locus on homologous chromosomes that code for different polypeptides

Question 4

What is a heterozygous genotype?

Answer 4

Having different alleles for a given gene (dominant and recessive pair/codominant pair)

Question 5

What is a homozygous dominant genotype?

Answer 5

Having two dominant alleles for a given gene

Question 6

What is a homozygous recessive gene?

Answer 6

Having two recessive alleles for a given gene

Question 7

What is the gene pool?

Answer 7

All the alleles in a population at any one time

Question 8

What is a genotype?

Answer 8

The genetic make up of an individual - all the alleles they possess

Question 9

What is a phenotype?

Answer 9

The observable characteristics of an organism determined by the genotype

If an organism is homozygous dominant or heterozygous, the dominant allele will always be expressed

Question 10

What is a test cross?

Answer 10

It is used to determine an unknown genotype when the dominant genotype is present

Question 11

How do you perform a test cross?

Answer 11

Cross the unknown phenotypically dominant plant with the recessive plant and look at offspring - are they all dominant offspring or is it a 1:1 ratio of dominant to recessive

Question 12

What is monohybrid inheritance?

Answer 12

The inheritance of a single gene

Question 13

Why did Mendel choose pea plants for his inheritance experiment?

Answer 13

• easy to grow
• can cross or self fertilise
• can produce fruits and flowers in the same year

Question 14

What does F1 and F2 mean?

Answer 14

F1 = first generation of offspring

F2 = second generation of offspring

Question 15

What is Mendel’s first law of inheritance?

Answer 15

The characteristics of an organism are determined by alleles, which occur in pairs
Only one allele of a pair is present in each gamete

Question 16

What is continuous variation?

Answer 16

When the characteristic has a range of values, is controlled by a number of genes (polygenic), and environmental factors have an effect

Normal distribution curve (bell shaped)

Question 17

What is discontinuous variation?

Answer 17

The characteristic has distinct categories controlled by a single gene, and environmental factors have no effect

Question 18

What is epigenetics?

Answer 18

When environmental factors influence the expression of a gene by, for example turning it on or off

Question 19

What is pure breeding?

Answer 19

Two organisms of the same phenotype that, when bred together, produce offspring with the same phenotype

Question 20

What is codominance?

Answer 20

A condition in which both alleles for a gene are expressed when present in a heterozygote

Both alleles are written with a capital letter

Question 21

What is complete dominance?

Answer 21

In codominance, when heterozygous individual expresses both alleles in the phenotype simultaneously without any blending (e.g. cattle coat colour)

Question 22

What is incomplete dominance?

Answer 22

Where heterozygous individuals produce a phenotype intermediate of the parental phenotypes (blending)

Question 23

What is dihybrid inheritance?

Answer 23

The inheritance of two unlinked genes

Independent assortment of these genes produces recombinants (different alleles in the gametes)

Question 24

What are the expected offspring ratios of two heterozygous codominant parents being crossed?

Answer 24

XY:Xy:xY:xy
9:3:3:1

Question 25

What is Mendel’s second law of independent assortment?

Answer 25

Either of a pair of alleles may combine randomly with either of another pair

Question 26

What is the expected (chi-squared)?

Answer 26

Based on ratios gained through genetic crosses - work out the expected offspring phenotype ratios before the genetic cross

Question 27

What is the observed (chi-squared)?

Answer 27

Actual ratios produced once the genetic crosses has been completed

Question 28

What is the null hypothesis?

Answer 28

There is no statistical significant difference between the expected ratios and the observed ratios and any difference is due to random chance

Question 29

What p value do we always compare to?

Answer 29

P=0.05 Compare to the critical value that has the same degrees of freedom to the number of phenotypes - 1

Question 30

When is the null hypothesis accepted?

Answer 30

- chi-squared is __ which is lower than the critical value of __ - so p>0.05, so there is more than 5% probability the difference is due to chance - therefore the difference is significant and the null hypothesis is accepted

Question 31

When is the null hypothesis rejected?

Answer 31

- chi-squared is __, which is higher than the critical value of __ - p<0.05, o there is less than 5% probability the difference is due to chance - difference is significant and the null hypothesis is rejected

Question 32

What is an autosome?

Answer 32

Any chromosome inside the nucleus that is not a sex chromosome

Question 33

What are sex chromosomes?

Answer 33

A chromosome concerned in determining the sex of an organism In humans, they are similar in one sex (females) and dissimilar in the other (males) In birds, they are similar in males, and dissimilar in females

Question 34

How many chromosomes do humans have and what are they?

Answer 34

Humans have 23 pairs of chromosomes The first 22 pairs are autosomes and the last pair are the sex chromosomes

Question 35

If a male with a sex-linked disease had a son, what are the chances if him having the disease?

Answer 35

Father cannot pass on the disease through the Y chromosomes Mother has to either be a carrier for, or have the disease themselves = only one recessive allele needed Father will not give him the disease

Question 36

If a male with a sex linked disease has a daughter, what are the chances of her having the disease?

Answer 36

All daughters can inherit the recessive allele from their father or mother, but require 2 recessive alleles for it to show in the phenotype

Question 37

What is haemophilia?

Answer 37

A sex linked disorder where the individual cannot produce enough of one particular blood plotting protein Symptom is slow, persistent bleeding H is the allele for normal blood clotting (dominant) h is the allele for haemophilia (recessive)

Question 38

What is duchess muscular dystrophy?

Answer 38

Sex linked disorder where the individual has a gene that doesn’t code for the protein dystrophin, which stabilises the cell membranes of muscle fibres Symptoms are loss of muscle mass and muscle weakness D = normal protein (functional) (dominant) d = mutant protein (not functional) (recessive)

Question 39

Why might there be a low number of children who have sex-linked disorders through affected parents?

Answer 39

- affected parent may die before they can reproduce - affected parent may decide they don’t wish to conceive and pass the condition on to their offspring

Question 40

What gametes can be produced by an organism with AaBb genotype that are found on difference chromosomes (not linked)?

Answer 40

AB Ab aB ab

Question 41

What gametes are produced by an organism with the genotype AaBb with genes that are found on the same chromosome (linkage)?

Answer 41

AB ab Complete linkage

Question 42

What gametes are produced by an organism with the genotype AaBb if crossing over has occurred because the genes are far apart (incomplete linkage)?

Answer 42

AB Ab = very low numbers aB = very low numbers ab Crossing over disrupts linkage only 5-10% of the time (during prophase I)

Question 43

What is complete linkage?

Answer 43

- genes are inherited together - crossing over is very unlikely to separate them as the genes are too close together on the same chromosome

Question 44

What is incomplete linkage?

Answer 44

- genes are on the same chromosome but are far apart - genes could be separated due to crossing ver and not be inherited together - rare (5-10% of the time)