How is inheritance explained?

Unit 2 Exam

Gene

Gene

The coded instructions for building a gene product.

(normally a protein but not always)

Allele

Slightly different forms of the same gene. One from each parent

Genome

All the genetic information in a cell, individual or species OR

All the genetic sequences within the haploid cells of the species

Chromosome

Contains the DNA, which contains the genes.

Chromatin

The stuff that chromosomes are made of

(DNA wrapped around histones)

DNA bases

Cytosine, Thymine, Adenine and Guanine

RNA bases

Cytosine, Uracil, Adenine and Guanine

Codon

Codons: the groups of 3 that RNA is read in. (base pairs with Anticodons)

Eg. (C,U,G)(A,G,A)

Anticodon

the groups of 3 that tRNA is read in. (base pairs with codons)

Eg. (G,A,C)(U,C,U)

Karyotype

Photograph of a person's chromosomes

Allele pairs of genes are located only on

homologous pairs of chromosomes

Advantage of sexual reproduction

Increases genetic diversity

Haploid

Having 2 of each chromosome. (A homologous pair)

Diploid

Having one of each chromosome

Telomere

The very end of the chromosome

Centromere

Middle of the chromosome, where the two sister chromatids link

Homologous Chromosomes

One chromosome that came from each parent, for the same gene.

Bivalents

A pair of homologous chromosomes help together at chaismata

Crossing over

Equivalent sections of non-sister chromatids break and are recombined, and in this way, genes are exchanged between homologous chromosomes. It increases genetic diversity

Chaismata

The point where homologous pairs cross over

Independent assortment

The randomness of organisation between non-homologous chromosomes. It increases genetic diversity

Purpose of meiosis

To take diploid cells and produce gametes that are haploid.

Early prophase I

During early prophase I, the nucleolus disappears, and the chromatin starts to condense and become visible.

Prophase I

The chromosomes continue to condense. The attach themselves to the inside of the membrane

Late Prophase 1

• The chromosomes move around the membrane to find their homologe.

• Homologous chromosomes cross over, and become anchored together at chiasmata.

Metaphase 1

bivalents assemble along the equator of the cell,  attached to the the spindle fibres.

Anaphase 1

The spindle fibres shorten, splitting each bivalent and dragging the homologous chromosomes to opposite poles of the cell by their spindle fibres.

Telophase 1

Chromosomes begin to condense, nuclear envelope may reform. A contractile ring forms, creating a cleavage furrow in the cell membrane.

Cytokinesis

Contractile ring constricts, creating two haploid cells

Interkinesis

Period of rest between phase 1 and phase two

Early prophase II

Chromosomes condense again. Centrioles separate and move toward opposite poles of the cell. A spindle of fibres begins to form between them. Each chromosome still consists of two sister chromatids (which may now be different to each other due to crossing over).

Metaphase II

The now haploid chromosomes line up along the equator of the cell

Anaphase II

Spindle fibres contract, separating the sister chromatids and dragging them to opposite poles of the cell.

Telophase II

Contractile ring contracts, forming a cleavage furrow. Nuclear membrane reforms. There are now 4 non-identical haploid cells

Genotype

The combination of alleles that you inherit. Eg. Bb, or BB or bb

Phenotype

The physical manifestation of the genotype. Eg. brown hair, blue eyes

Homozygous

Having two identical alleles of a particular gene

Heterozygous

Having two different versions of the same gene

Dominant trait

The trait expressed in the phenotype

Recessive trait

Trait not expressed in the phenotype

Complete Dominance

A recessive phenotype paired with a dominant phenotype, so only the dominant phenotype is visible. Eg. Bb

Codominance

When both alleles are seperatly expressed in the phenotype.

Eg. B^r B^w

Incomplete Dominance

When both alleles are together in the phenotype. Eg. B^ B^w