D3.2 Inheritance

Gene

short section of DNA that codes for a protein

Allele

An alternative version of a gene.

Genotype

Combination of inherited alleles

Phenotype

the set of observable characteristics of an organism resulting from the interaction of its genotype with the environment.

Dominant allele

allele will always be expressed if present

Recessive allele

allele will always be expressed if 2 copies are present

Heterozygous

2 different alleles present in the genotype

Homozygous

2 copies of the same allele

Phenotypic plasticity

Physical changes in our appearance as a response to adapting to changes in the environment.

-usually reversible changes

How is a diploid zygote formed?

Haploid cells (with a single copy of a gene) produced by each parent fuse to form a diploid zygote with an equal amount of genetic information from both parents

When sperm fertilizes an egg

Genetic crossing in flowering plants

Male (stamen) and female (pistil) gametes are often present in the same plant.

Occurs during pollination

Methods: selecting the pollen from one plant and brushing it onto the stigma of another plant.

Determination of sex in humans

The sperm because the sperm can carry either the Y or X chromosome

XX

girl

XY

boy

Example of a recessive genetic disease

PKU: A recessive genetic condition caused by a mutation in an autosomal gene (chromosome 12) that codes for the enzyme needed to convert Phe to Tyr, leading to toxic buildup of Phe in the bloodstream of an individual.

Explain the ways that members of the same species can have variety in the gene pool.

SNP's due to changes in a single nucleotide sequence, resulting in many different alleles for a single gene

What is SNPs

Positions in a gene where bases are different.

What are antigens?

types of proteins used to recognize cells.

usually used to fight off diseases & attack them.

Inheritance of different blood types

-the gene is called the ABO gene.

- three allelic forms A, B and O

- A and B are dominant

-O is recessive

Which blood type has no antigens?

O has no antigens therefore it is universal; when inserted into our body our body doesn't detect it and doesn't attack it.

Co-dominance

A condition in which both alleles for a gene are fully expressed in the phenotype

Incomplete dominance

Both alleles are expressed, and rather than two phenotypes expressed, you get a third phenotype of both alleles mixed

Example of a sex-linked genetic disorder

Haemophilia

- in haemophilia, blood doesn't clot properly, which makes it difficult to control bleeding

- sex-linked condition because the genes controlling production of these blood proteins are located on the X chromosome.

- Haemophilia is caused by a recessive allele.

- haemophilia is largely a disease of the male

Discrete variation

when the expression of the phenotype is often caused by a specific gene and can rarely be altered or changed

eg. ABO blood groups

continuous variation

when the phenotype is affected by environmental factors

many genes interactin with each other and the environment. cannot be easily categorized.

eg. Skin colour

- often illustrated using box and whisker plots

How to make a box and whisker plot

1. Draw a vertical scale to include the lowest and highest data values.

2. To the right of the scale, draw a box from Q1 to Q3

3. Include a solid line through the box at the median level.

4. Draw vertical lines, called whiskers, from Q1 to the lowest value and from Q3 to the highest value.