20 - Patterns of Inheritance and Variation

Question 1

How is closeness of two linked genes on a chromosome linked to the number of recombinant offspring?

Answer 1

More closely linked genes means less separation and so less recombinant offspring

Question 2

What is a phenotype?

Answer 2

Physical characteristics of an organism

Question 3

What is a genotype?

Answer 3

Genetic makeup of an organism

Question 4

What 2 things affect an organism’s phenotype?

Answer 4

Genotype and environment

Question 5

What is it called when a characteristic is codes for by multiple genes?

Answer 5

Polygenic

Question 6

What type of characteristics tend to be polygenic?

Answer 6

Ones which vary within a range, such as height

Question 7

What is continuous variation?

Answer 7

A characteristic that can take any value within a range

Question 8

What is discontinuous variation?

Answer 8

A characteristic that can only result in certain values

Question 9

What does it mean if something is monogenic?

Answer 9

Controlled by only 1 gene

Question 10

What type of characteristics tend to be monogenic?

Answer 10

Ones which exhibit discontinuous variation

Question 11

What are the 3 things which affect genotype?

Answer 11

1. Sexual reproduction 2. Gene mutations 3. Chromosome mutations

Question 12

What 2 characteristics do all mutations which take place during gamete formation have?

Answer 12

1. Persistent (passed through many generations) 2. Random (so not directed by need)

Question 13

When do chromosome mutations occur?

Answer 13

During meiosis

Question 14

What is polyploidy?

Answer 14

A condition in which an organism has more than two complete sets of chromosomes

Question 15

What type of organism tends to be polyploidy?

Answer 15

Many cultivated plants

Question 16

What are 3 ways in which sexual reproduction can cause genetic variation?

Answer 16

1. Allele shuffling during crossing over 2. Independent assortment 3. Random fertilisation, where any male gamete can fertilise any female gamete

Question 17

What is etiolation?

Answer 17

Where plants grow long and spindly due to a lack of light

Question 18

What is chlorosis?

Answer 18

The yellowing of leaves due to a lack of Magnesium ions (Mg2+)

Question 19

What are 3 examples of environmental factors which can affect phenotype?

Answer 19

1. Diet in humans 2. Etiolation 3. Chlorosis

Question 20

What is a dominant allele?

Answer 20

An allele which will always be expressed when present

Question 21

What is a recessive allele?

Answer 21

One which will only be expressed when there are 2 copies present

Question 22

What does it mean if alleles are codominant?

Answer 22

Both are expressed in the phenotype, which becomes sort of a hybrid of the traits coded for by both

Question 23

What is a dihybrid?

Answer 23

A hybrid that is heterozygous for alleles of two different genes

Question 24

How do you write the first and second generations when doing homozygous genetic crosses?

Answer 24

First is F1, second is F2

Question 25

What do you call the parental generation when doing a homozygous genetic cross?

Answer 25

F1 generation

Question 26

What is a gene locus?

Answer 26

Location of a gene on a chromosome

Question 27

What are the 3 golden rules of monohybrid crosses?

Answer 27

1. Homozygous dominant and homozygous recessive give 100% heterozygous offspring 2. Two heterozygous give a 3:1 ratio of phenotypes 3. Heterozygous and homozygous recessive give a 1:1 ratio of phenotypes

Question 28

What is a test cross?

Answer 28

Crossing an organism with a heterozygous genotype with one with a homozygous recessive genotype

Question 29

What would you use a test cross for?

Answer 29

Determining the genotype of an individual showing a dominant characteristic

Question 30

What happens when multiple (i.e. more than 2) possible alleles are present for a gene?

Answer 30

Only 2 can be present in the offspring's genotype

Question 31

Which gamete determines the sex of the offspring?

Answer 31

Sperm, depending on whether it carries a Y allele or not

Question 32

What does it mean if a gene is sex linked?

Answer 32

Located on one of the sex chromosomes

Question 33

What is an autosome?

Answer 33

Any chromosome that is not a sex chromosome

Question 34

What is autosomal linkage?

Answer 34

Gene loci present on the same autosome that are often inherited together

Question 35

What are 3 examples of sex-linked medical conditions?

Answer 35

1. Haemophilia 2. Colour blindness 3. Duchenne's muscular dystrophy

Question 36

What is dihybrid inheritance?

Answer 36

The inheritance of two characteristics which are controlled by different genes

Question 37

What are 2 reasons the actual ratio of phenotypes may differ from the theoretical one?

Answer 37

1. Fertilisation of gametes is a random process, so few chance events can lead to a skewed ratio 2. Genes being studied are on the same autosome

Question 38

What is epistasis?

Answer 38

When one gene masks or suppresses the expression of another

Question 39

Why are sex-linked recessive conditions more likely to appear in men?

Answer 39

As there is no dominant allele on the X chromosome

Question 40

What is the usual phenotypic ratio you would expect for a dihybrid cross?

Answer 40

9:3:3:1

Question 41

What happens to the phenotypic ratio of a dihybrid cross if there is autosomal linkage?

Answer 41

It becomes more like a monogenic one (3:1)

Question 42

What is the Chi Squared test used to measure?

Answer 42

The size of the difference between the observed and expected results, as well as whether these differences are significant

Question 43

How do linked genes tend to be inherited?

Answer 43

Together, unless they are separated by chiasmata

Question 44

What are recombinant offspring?

Answer 44

Recombinant offspring are those that have an arrangement of alleles on the chromosome that was not present in either parent

Question 45

What are the 2 forms of epistasis?

Answer 45

Dominant and recessive epistasis

Question 46

When would recessive epistasis occur?

Answer 46

If the presence of 2 recessive alleles led to a lack of something

Question 47

What is inbreeding?

Answer 47

Mating between closely related individuals

Question 48

What is outbreeding?

Answer 48

The breeding of distantly related individuals of a species