Inheritance

Question 1

Genotype

Answer 1

The genetic constitution of an organism eg, all the alleles

Question 2

Phenotype

Answer 2

The expression of the genotype and its interaction in the environment

Question 3

Allele

Answer 3

A specific version of the same gene

Question 4

Gene

Answer 4

Base sequence in a section of DNA that encodes for AMINO ACID SEQUENCE OF a polypeptide or functional RNA

Question 5

Locus

Answer 5

Where a particular gene is located on a pair of homologous chromosomes

Question 6

Chromosome

Answer 6

A molecule of DNA wrapped around histone proteins

Question 7

Homologous chromosomes

Answer 7

Contain the same genes at the same loci, but may have different alleles

Question 8

Are homologous chromosomes the same length?

Answer 8

Yes because they have the same genes at the same loci
But sex chromosomes are different length: only homologous at a specific sequences of bases that’s the same

Question 9

Pair of Alleles at the same loci in a homologous pair do what?

Answer 9

Encode for a characteristic (based on amino acid sequence of a polypeptide chain) depending on the nature of the 2 alleles
Because they are the same gene encode for the same characteristic

Question 10

What can each allele in a homologous pair be?

Answer 10

Dominant
Recessive
Co dominant

Question 11

Dominant alleles

Answer 11

This allele will be expressed in the phenotype regardless of the nature of the other allele
Eg, will encode for the specific amino acid sequence in the polypeptide always

Question 12

Recessive alleles

Answer 12

An allele only expressed in the phenotype if the other allele (at the same locus in a homologous pair) is also recessive

Question 13

Co dominant alleles

Answer 13

When the 2different alleles in a homologous pair are both expressed in the phenotype

Question 14

Homozygous

Answer 14

When the 2alleleles in a homologous pair are the SAME eg both recessive or both dominant

Question 15

Heterozygous

Answer 15

When the 2 alleles in a homologous pair are different eg one is recessive and one is dominant

Question 16

What is a mono hybrid cross used for?

Answer 16

To breed together 2 organisms to study the inheritance of 1 particular gene

Question 17

In Gametes, how many alleles of a gene is there?

Answer 17

1 allele because in a gamete there are no homologous chromosomes, just 1 chromosome
So this chromosome will only have 1 allele for a gene

Question 18

Punnet squares

Answer 18

When 2 organisms are bred together, write both their genotypes in a cross to work out the possible genotypes offspring’s can have (and ratio of what is most likely to inherit)

Question 19

How could you prove an organism has a given genotype?

Answer 19

By using a test cross
breeding with another organism (recessive one we know the genotype for) and if an offspring with a specific genotype is produced then we can work it out

Question 20

Why are the offspring produced’s genotypes not follow the ratio we calculated using punnet squares?

Answer 20

Because of random fusion of gametes, so the actual ratio of gametes is affected heavily by chance

Question 21

Punnet square of a mono hybrid cross

Answer 21

2 by 2
Studying 1 gene, only 2 alleles of each organism’s homologous chromosomes can be studied
It’s only possible to have 2 alleles of 1 gene in a homologous pair

Question 22

What is a di hybrid cross?

Answer 22

Breeding together 2 organisms to study the inheritance of alleles from 2 DIFFERENT genes

Question 23

Gametes in a dihybrid cross

Answer 23

Every gamete will have 1 allele from 1 of the genes, then 1 allele for the other gene
Because gametes don’t have homologous chromosomes so cannot have more than 1 allele of each gene

Question 24

How many possible gametes from each organism in a di hybrid cross ?

Answer 24

4 per organism
Each having 1 allele from 1 gene, and 1 allele from a DIFFERENT gene

Question 25

How many possible gametes in a mono hybrid cross?

Answer 25

2 per organism because 1 gene is studied, so it’s 1 allele in 1 gamete and the other allele of the SAME GENE in the other gamete

Question 26

Independent segregation of chromosomes

Answer 26

It is random what way the homologous chromosomes separate in meiosis, the chromosomes do not influence how each other divide The combination of maternal and paternal chromosomes in a gamete is completely random

Question 27

Dihybrid cross punnet square

Answer 27

4 gametes possible from mother on one axis Same for the other =16 possible combinations of alleles for the 2GENES

Question 28

Possible genotypes in a dihybrid cross mist be written…

Answer 28

So alleles of the same gene are written together Capital (dominant) allele first then recessive lowercase one

Question 29

Cross

Answer 29

Breed together

Question 30

How are co dominant alleles written?

Answer 30

With a capital letter to represent the same gene Then an uppercase letter superscript to show the different allleles ALL capital as both alleles are expressed in the phenotypen

Question 31

Can genes have more than 2 alleles?

Answer 31

Yes but in a pair of homologous chromosomes, you can only have maximum of 2 different alleles

Question 32

How are multiple alleles of the same gene written?

Answer 32

Capital letter to represent the gene Superscript to show the different alleles

Question 33

Sex linkage

Answer 33

Genes located on a sex chromosome eg X or Y

Question 34

Sex chromosomes

Answer 34

X and Y

Question 35

Non sex chromosomes

Answer 35

Autosomes

Question 36

Carrier

Answer 36

For diseases caused by recessive alleles: someone is heterozygous for this allele so the disease is not expressed in the phenotype but they carry the allele for ir

Question 37

For sex linked chromosome, can a father with the allele pass it on to his son?

Answer 37

No because the allele is on the X chromosome and a father gives the son the Y chromosome

Question 38

For sex linked recessive allele on the X chromosome, why is it more likely for men to have the allele?

Answer 38

Because they only require 1 allele to express this in th phenotype as they only have 1 X chromosome whereas women require 2 recessive alleles on both X chromosomes

Question 39

Autosomal linkage

Answer 39

When 2 or more genes are located on the same non sex chromosome (autosome)

Question 40

Does independent segregation affect autosomal linkage?

Answer 40

No because the genes are on the same chromosome so when the homologous chromosomes separate, they will still be together on the same chromosome

Question 41

Does crossing over affect autosomal linkage?

Answer 41

Yes

Question 42

Crossing over

Answer 42

When different alleles on a homologous pair (eg within non sister chromatids) switch to form recombinant chromosomes with a new combo of alleles

Question 43

How to represent autosmally linked chromosomes

Answer 43

Write the alleles on top of each other (in a punnet square, in gametes etc)

Question 44

Effect of crossing over of autosomally linked chromosomes in meiosis?

Answer 44

Form RARE recombinant chromosomes aka unique combos of alleles in a chromosome that means the punnet square is extended to show the new possible combos of alleles

Question 45

Epistaxis

Answer 45

The study of how genes interact with each other

Question 46

Why are there differences in observed and expected ratio of phenotypes?

Answer 46

Small sample size Random fertilisation so combination of alleles in a homologous pair is affected by chance Crossing over occurs (rare) Unexpected interaction between alleles (epistasis)

Question 47

Crossing over mechanism

Answer 47

Before meiosis 1, homologous chromosomes pair up = bivalent Form a chiasmata And equal lengths of chromosomes between non sister chromatids are exchanged = recombinant chromosomes with unique combo of alleles

Question 48

Pure breeding meaning

Answer 48

Organism is homozygous for alleles of a gene In both homologous chromosomes, has same allele for that gene

Question 49

Calculating percentage of offspring with specific phenotype

Answer 49

Number of organisms with this phenotype worked out from cross/ number of organisms with a phenotype THAT SURVIVE PAST BIRTH Not always every single genotype will survive so not included in possible phenotypes

Question 50

Why do we know if allele is recessive or dominant

Answer 50

When crossed: If phenotype is expressed in first generation the alleles for this phenotype are probably dominant And if the allele frequency is much higher its dominant likely because only 1 copy needed for expression