Topic 14 Genotypes and Phenotypes

Question 1

What is a phenotype?

Answer 1

The visible, measurable expression of the genetic makeup of an organism’s structure or functioning.

Question 2

What is a genotype?

Answer 2

The underlying genetic makeup that determines an organism’s phenotype.

Question 3

What does homozygous mean?

Answer 3

When both chromosomes contain some copies of the allele for the particular trait, either homozygous dominant or recessive.

Question 4

What does heterozygous mean?

Answer 4

When an organism inherits two different Alleles for a trait and the dominant allele is expressed.

Question 5

What does hemizygous mean?

Answer 5

Refers to the genotype of the human male in relation to any gene carried on either the X or Y chromosome and which for each gene comprised only one allele.

Question 6

What are autosomal genes?

Answer 6

A gene that is found in two copies, inherited from your mother and father, a gene that controls one function can exist n multiple forms or variants.

Question 7

What are genes on the X chromosome?

Answer 7

• because of their size differences the X chromosome has more gene loci that the Y chromosome.
• genes that are located on the X chromosome and are not represented on the Y chromosome must be inherited by females in two copies of that particular allele, males are affected if they have just one allele so males more commonly show that trait.
• when a gene is located on the sex chromosome, the traits controlled by its alleles do not appear equally in both sexes.

Question 8

What are genes on the Y chromosome?

Answer 8

• small segments of DNA at each ends of the Y chromosomes are homologous with DNA segments on the X chromosome. During prophase of meiosis homologous chromosomes synapse in preparation for migrating to opposite poles of the spindle. The presence of regions of the y chromosome that are homologous to regions on the X chromosome means that during meiosis in males the sex chromosomes can pair up and then separate correctly
• more than 95% of DNA on the Y chromosome is unique, this consists of 59 genes which control production of proteins that produce male characteristics such as testis formation.

Question 9

What is complete dominance?

Answer 9

Dominant refers to an allele that expresses its phenotype in the homo and heterozygous forms, recessive refers to an allele that does not express its phenotype unless in the homozygous form. The term carrier refers to a heterozygous that has the allele for a recessive trait but does not show the trait,

Question 10

What does co dominance refer to?

Answer 10

When both alleles are expressed in the phenotype in the heterozygous conditions

Question 11

What environmental factors affect genes?

Answer 11

Wind exposure, water availability, avidity, temperature soil type light and predation

Question 12

What are monogenic traits?

Answer 12

• variation that occurs in individuals of a species due to the action of difference alleles of a particular gene
• when a gene has two alleles and the traits are dominant or recessive there are only two variation in phenotype in the population, or three or mo when a gene has three alleles.

Question 13

What is discontinuous variation?

Answer 13

When member of a population can be classified into a few discrete and Nin overlapping classes, monogenic traits show discontinuous variation.

Question 14

What are polygenic traits?

Answer 14

Variation is caused by the action of two or more genes at difference loci, the genes involved are called polygenic are their expression is also influence by environmental factors.

Question 15

What does continuous variation refer to?

Answer 15

When member of a population cannot be classified into a few distinct groups, they show a variety of phenotypes. Polygenic traits show discontinuous variation, in quantitative values.

Question 16

What number of steps need to be followed in order for change to occur in a species?

Answer 16

1. There must exist variation in characteristics within the species (original changes in species via mutation)
2. Differential survival, a selective pressure or agent selects for characteristics which equips an individual of the species to survive better in its environment over other members of the species with different characteristics.
3. Genetic inheritance: those individuals that have characteristics that allow them to surge have a selective advantage. They will reproduce and pass on the genes that code for those characterises to the next generation. These individuals have more offspring.
4. Within time, the frequency of individuals with the advantageous characteristics will increase in the population, provided rant the selective pressure or agent is still active, causing change in population over time.

Question 17

What is epigenetics?

Answer 17

Epigenetics refers to all changes to genes apart from changes to their base sequences, which bring about phenotypic changes. Epigenetic factors can bring about these changes, which act on DNA to turn genes permanently on or off.

Question 18

What are epigenetic factors?

Answer 18

Epigenetic factors can change how DNA in cells is packages or how it is labelled. Genes in segments of DNA that are tightly packaged are silenced, genes in segments of DNA with open packaging are active in transcribing polypeptide gene products.

Question 19

How can DNA be labelled?

Answer 19

Labelling DNA is like adding a tag that does not alter the base sequence of genes but can either silence or make genes active.
Methyl groups are epigenetic tags which can be added to any c base alongside a g base in DNA.
Active genes are found to have fewer methyl groups that inactive gene, so tagging genes by the addition of methy groups can change gene expression and permanently switch those genes off.