3.4 Genes

Question 1

Chromosome

Answer 1

A bundle of DNA containing many genes

Question 2

Alleles

Answer 2

Different versions of the same gene

Question 3

Phenotype

Answer 3

Physical appearance
(blue eyes)

Question 4

Genotype

Answer 4

The combination of alleles which you carry for a particular gene

Question 5

Dominant allele

Answer 5

An allele which is always expressed when it is present
- Capital letter

It cannot be masked by another allele

BB or bB or Bb

Question 6

Recessive allele

Answer 6

An allele which can be masked by another allele
- small letters

it is only expressed when two copies are present.

must be bb, no B

Question 7

Homozygous

Answer 7

Individual has two copies of the same allele of a gene on a pair of chromosomes
(same)

Question 8

Heterozygous

Answer 8

Individual has two different alleles of a gene on a pair of chromosomes
(other)

Question 9

Diploid cells

Answer 9

A cell which contains two copies of each chromosome

Question 10

haploid cells

Answer 10

A cell which contains one copy of each chromosome

Question 11

production of sperm cells and ova occurs through…

Answer 11

meiosis

Question 12

Inheritance of eye colour

Answer 12

Alleles of sperm and ova determine phenotype of baby

Same rule applies to inheritance of plants

If there was a dominant allele (B) eye color would show dominant (brown)

Question 13

Dominant alleles are twice as likely to be shown…

Answer 13

Question 14

Ratio of
RR : Rr : rr

Answer 14

1 : 2 : 1
25%, 50%, 25%

Question 15

Ratio of
RR : Rr : rr

Answer 15

RR : Rr : rr = 1 : 2 : 1
RR : Rr : rr = 25%, 50%, 25%

Question 16

in the genetic cross Rr x Rr, what is the ratio of phenotypes?

Answer 16

Dominant : Recessive = 3 : 1

Question 17

Drawing a punnet sqaure

Answer 17

1. Write down the genotypes of the parents (Rr x Rr)
2. Write down the genotypes of the gametes that each parent produces. (R +r) & (R +r)
3. Draw your Punnett Square
4. Fill it in

This shows you the possible genotypes of the offspring

Must draw a key for what the Phenotypes are

Question 18

Carrier

Answer 18

a heterozygous genotype which shows the dominant phenotype is a carrier for an allele which is not expressed in the phenotype

Aa
- Shows A, but is a carrier for a

Question 19

Test cross

Answer 19

An experimental cross of an individual organism of dominant phenotype but unknown genotype to an organism with a homozygous recessive genotype
AA x aa → all normal pigment (Aa)

EG - photo
The male has one of two genotypes : BB or Bb. This male is crossed to a black-bodied female of genotype bb. There are two possible outcomes:

Question 20

Mendels discovery

Answer 20

He crossed pea plants and dicovered the basic princeples of heredity with the idea of ‘dominant’ and ‘ressesive’ genes.

Disocvered:
- organisms possess two versions of each factor
- Parents contribute equally to the inheritance of offspring as a result of the fusion between randomly selected egg and sperm

Question 21

Co-Dominance

Answer 21

2 diffrerent alleles show up in 1 phenotype
- both alleles are dominant and show in phenotype

Question 22

Inheritance of ABO blood groups

Answer 22

A blood = Carbohydrate A attached
B blood = Carbohydtate B attached
O blood = Neither carbohydrate

Use Punnet square to solve which blood type baby may inherit from parents *

Question 23

Inheritance of cystic fibrosis and Huntington’s disease

Answer 23

Cystic fibrosis:
- autosomal recessive disorder caused by a mutation to the CFTR gene on chromosome 7
- mucus clogs the airways and secretory ducts of the digestive system, leading to respiratory failure and pancreatic cysts
- CAN be a carrier

Huntington’s Disease:
- autosomal dominant disorder caused by a mutation to the Huntingtin (HTT) gene on chromosome 4
- Symptoms of Huntington’s disease include uncontrollable, spasmodic movements (chorea) and dementia
- CANNOT be a carrier

Question 24

Inheritance of Sickle-cell disease

Answer 24

Autosomal recessive
- Makes blood cells shaped like sickles
- Causes blood clots

75% have

Question 25

sex-linked diseases

Answer 25

characteristic is located on a sex chromosome (X or Y)

Y chromosome much shorter - 78 genes
X chromsome longer - 2000 genes

Question 26

Pattern of inheritance on sex linked chromsomes

Answer 26

As human females have two X chromosomes (and therefore two alleles), they can be either homozygous or heterozygous
- X-linked dominant traits are more common in females (twice chance to have one)

Human males have only one X chromosome (and therefore only one allele) and are hemizygous for X-linked traits
- X-linked recessive traits are more common in males (cannot be masked by another allele)

Red = disease

Question 27

Red-green colour blindness and haemophilia

Answer 27

Haemophilia:
- recessive sex-linked trait
- body’s ability to control blood clotting is impaired
- fibrin formation is prevented due to defective coagulation factors on the X chromosome

Red-Green Colour Blindness:
- recessive sex-linked trait
- caused by a mutation to the red or green retinal photoreceptors on the X chromosome
- diagnosed using the Ishihara colour test (circles and colours showing a number)

Question 28

Radiation and mutagenic chemicals

Answer 28

increase the mutation rate and can cause genetic diseases and cancer
- The nuclear bombing of Hiroshima and accident at Chernobyl are two examples of a catastrophic release of radioactive material

Question 29

Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl

Answer 29

long-term consequences:
- increased incidence in cancer development
- Reduced T cell counts and altered immune functions, leading to higher rates of infection
- organ-specific health effects

Question 30

Pedigree charts

Answer 30

graphic representations of inheritance in a family

2 affected must have affected off spring

Question 31

Determining a recessive trait with pedigree charts

Answer 31

Skips a generation

Question 32

Determining a Dominant trait with pedigree charts

Answer 32

Most likely dominant due to trait in all generations

Question 33

Identifying autosomal dominant with pedegree charts

Answer 33

Question 34

Identifying autosomal recessive with pedegree charts

Answer 34

If both parents are unaffected and an offspring is affected, the trait must be recessive
- Both male and females affected

Question 35

Identifying Sex linked with pedegree charts

Answer 35

usually only male affected
- not possible to confirm sex linkage from pedigree charts, as autosomal traits could potentially generate the same results