Inheritance | 17

Question 1

Gamete

Answer 1

A gamete is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually

(Egg / sperm cell)

Question 2

Inheritance

Answer 2

the transmission of genetic information from parents to offspring

Question 3

Chromosome

Answer 3

a thread-like structure of DNA that carries genetic information in the form of genes.

Question 4

Gene

Answer 4

a length of DNA that codes for a particular protein

Question 5

Allele

Answer 5

one of a number of different versions of a gene

Question 6

Genotype

Answer 6

the genetic makeup of an organism, consisting of all the alleles present.

Question 7

Phenotype

Answer 7

the observable features of an organism as a result of the expression of particular alleles of the gene.

Question 8

Homozygous

Answer 8

an organism containing two identical alleles of a particular gene

Question 9

Heterozygous

Answer 9

an organism containing two different alleles of a particular gene.

Question 10

Diploid cells

Answer 10

nuclei which contain a full set of chromosomes (23 pairs)

Question 11

Haploid Cells

Answer 11

nuclei which only contain half the number of chromosomes. These cells are egg and sperm cells, which fuse during fertilization to produce a diploid cell.

Question 12

Chromosomes in diploid cells

Answer 12

There are 23 pairs of chromosomes in the nucleus of all diploid human cells.

One of these pairs determine gender.

These chromosomes are therefore called the sex chromosomes.

For females these chromosomes are XX and for males the chromosomes are XY.

All female egg cells contain only an X chromosome, whereas male sperm cells may contain an X or a Y, thus the gender of the baby depends on which sperm cell fertilizes the egg cell

Question 13

Mitosis

Answer 13

Mitosis is a form of cell division.

During mitosis, nuclear division of a parent cell occurs, producing two genetically identical daughter cells.

Mitosis is used to create new cells in the body to repair and replace old and damaged tissues, as well as allowing growth of the organism and playing a role in asexual reproduction.

Mitosis involves the splitting of chromosomes into their two halves, each of which are known as a chromatid

Question 14

Steps of mitosis

Answer 14

1. Before replication can occur, the chromatids in the parent cell must replicate to produce identical copies of themselves which pair as chromosomes.
2. The chromosomes line-up along the nucleus.
3. The chromosomes separate so that each identical chromatid is pulled to opposite poles of the cell.
4. The cell membrane constricts in the middle and the nucleus is separated as the cell splits into two new daughter cells. Each of these cells will contain a set of chromatids, which then replicate themselves again to produce new chromosomes.

Question 15

Stem cell

Answer 15

Stem cells are found in embryos or in the bone marrow.

These cells are unspecialized and divide by mitosis to produce daughter cells which then specialize to have a variety of functions.

Cells, once specialized, cannot produce unspecialized cells. For example, a cell which makes up the heart tissue cannot divide to make a cell which can act as skin tissue as the cell produced will already be specialized as a heart cell

Question 16

Meiosis

Answer 16

Meiosis is used to make four genetically unique daughter cells and is used in the production of gametes.

During meiosis, the chromosome number is halved, and a diploid cell divides to produce four haploid cells.

As each gamete produced is genetically unique, each of the offspring will also be unique.

This is beneficial for a species as it produces genetic variation.

Question 17

Monohybrid inheritance

Answer 17

Offspring inherit characteristics from both their mother and father and two sets of genes are inherited, one from each.

If the mother and father pass down the same allele for a particular trait, e.g. they both pass down the allele for blue eyes, the offspring will have two identical alleles for this trait, which is referred to as homozygous.

If two separate alleles are passed down, e.g. the mother has blue eyes and the father has brown eyes, the offspring will have two different alleles for the gene, which is called heterozygous.

If two identical homozygous individuals are bred together, it is referred to as pure-breeding and the offspring will have the same characteristics as the parents.

Breeding heterozygous parents is not pure-breeding, as there are a number of different alleles that the offspring could display in their phenotype

Question 18

Dominant and recessive alleles

Answer 18

Alleles can be dominant and recessive.

A dominant allele is always expressed if present, whereas the recessive allele is only expressed in the absence of the dominant allele. For example, the allele for brown eyes is dominant and the allele for blue eyes is recessive. This means that if two parents with blue and brown eyes were bred, the offspring would have brown eyes as this allele is dominant.

Question 19

Co - dominance

Answer 19

Some alleles are co-dominant, meaning that neither is recessive, and they are both displayed in the phenotype.

An example of this is blood groups. The three possible alleles for blood groups are A, B and O. The A and B alleles are co-dominant, which leads to the AB blood group. O is recessive, and thus is only displayed in the phenotype if both parents have O blood groups.

Question 20

Sex linked characteristics

Answer 20

Some genes are located on the sex chromosomes.

A characteristic which comes from one of these genes is referred to as a sex-linked characteristic.

A result of this is that some traits are more common to one gender, for example any gene located on the Y chromosome can only be present in males as females do not have this chromosome.

An example of a sex-linked characteristic is color blindness, which is a recessive characteristic found on the X chromosome.