End of Unit - Genetics

Biology end of unit test (march 4th)

Advantages of asexual reproduction

• Only one parent is needed

• Uses less energy

• Faster - don't need to find a mate

Disadvantages of asexual reproduction

• No variation in population because the offspring are genetically identical to the parent

• Means if the environment changes the whole population is affected - same with disease

Advantages of sexual reproduction

Produces variation in offspring, meaning if the environment changes it is likely that some organisms in the species will have good characteristics to survive - over time this leads to natural selection

Disadvantages of sexual reproduction

• Takes time and energy to find a mate

• Isolated individual can't reproduce

What experiment did Mendel do

• Mendel studied how characteristics are passed on from plant to plant

• In his first experiment, he crossed a tall pea plant with a dwarf pea plant

• in his second experiment, he crossed two tall pea plant offspring

What did Mendel conclude

• Offspring have some characteristics that their parents have because they inherit ‘hereditary units’ from each.

• One unit is received from each parent.

• Units can be dominant or recessive, and cannot be mixed together.

Explain why there are differences in the inherited characteristics as a result of alleles

• Alleles (different forms of the same gene) lead to differences in inherited characteristics.

• This is because different alleles code for different forms of the same protein

• an allele that codes for a damaged form of a protein can cause illness.

Define chromosome

A structure found in the nucleus which is made up of a long strand of DNA.

Define gene

A section of DNA that codes for a protein

Define allele

Different versions of the same gene

Define dominant

An allele that is always expressed, even if the individual only has one copy

Define recessive

An allele that needs two copies to be expressed

Define homozygous

when an individual has two of the same allele for a gene

Define heterozygous

When an individual has two different alleles for a gene

Define genotype

The combination of two alleles that an individual possesses for each gene

Define phenotype

The physical expression of the genotype

Define gamete

An organism’s reproductive cell

Define zygote

A fertilised egg cell

Describe how the sex of offspring is determined at fertilisation

• Men have X and Y chromosomes.

• Women have two X chromosomes.

• XX combination allows female characteristics to develop.

• Equal chances of having boy and girl.

Describe the inheritance of ABO blood groups

• inheritance of blood groups is an example of codominance

• three alleles determine blood group inheritance instead of two

• alleles I^A and I^B are both codominant

• they are both dominant to I^O

• I^A results in production of antigen A in the blood

• I^B results in production of antigen B in the blood

• I^O results in no antigens being produced in the blood

Describe how sex-linked genetic disorders are inherited

• Y chromosomes miss some genes found in the x chromosome.

• This means a man (XY) will have only one allele for some genes on the X chromosome (because those genes are missing on the Y chromosome).

• If the allele for on of these X chromosome genes causes a genetic disorder, the man will develop this.

• The allele a man has in the X chromosome, dominant or not, will always be expressed (since there is only one)

What are most phenotypic features the result of

Most phenotypic features are the result of multiple genes rather than single gene inheritance.

Describe the causes of variation that influence phenotype including genetic variation

• Different characteristics can arise as a result of random mutation, and sexual reproduction

• Random mutation occurs in gametes to produce offspring with brand new characteristics

• Sexual reproduction causes the offspring to have a combination of characteristics from mother and father

Describe the causes of variation that influence phenotype including environmental variation

• Characteristics can also be caused by an organism's environment

• For example a child who does receive adequate nutrition will not grow to their full height

• these changes are not heritable

Outcomes of the Human Genome Project

1. Helped scientists to discover which genes predispose people to certain diseases

• Doctors could provide more specific advice on the best lifestyle and diet to help people delay the onset of diseases, or avoid them entirely

2. allowed doctors to design new dugs specifically tailored to those with genetic variation

3. Finally, allows doctors to identify which faulty alleles cause inherited disorders

There is usually ____ within a population of a species, and  _____

there is usually extensive genetic variation within a population of a species, and these arise through mutations

Do mutations affect the phenotype

• Most genetic mutations have no effect on the phenotype

• Some mutations have a small effect on the phenotype

• It is rare for a single mutation to significantly affect the phenotype