Genetics and Inheritance Year 10 Biology

Part 3:

Predicting Possibilities

Your Genotype & Phenotype make you who you are!

2.Genes are passed on from one generation to the next!

Predicting possibilities

Shows which alleles for a particular trait are present in the gametes of each parent.

Shows possible ways in which these alleles can be combined.

3.Genes are passed on from one generation to the next!

A Punnett square is a diagram that is used to predict the outcome of a genetic cross.

Punnett square rules

The alleles in each of the parent’s genotypes for that trait are put in the outside squares and then multiplied together to show the possible genotypes of the offspring.

Inheritance is complete dominance: capital letter for the allele of the dominant trait (e.g. B) and a lower-case version of the same letter for the allele for the

If the type of inheritance is incomplete or codominant, then different letters are used to represent them (e.g. R and W or IAand IB ).

The sex chromosomes are included when an X-linked trait is involved (e.g. XB Xb and XB Y).

4.Genes are passed on from one generation to the next!

Complete Dominance5.Genes are passed on from one generation to the next!

Complete Dominance

6.Genes are passed on from one generation to the next!

Punnett Square7.Genes are passed on from one generation to the next!

Punnett squares show us the chance of offspring inheriting particular combinations

Pedigree Charts8.Genes are passed on from one generation to the next!

A diagram that shows a family’s relationships and how characteristics are passed on from one generation to the next is a pedigree chart.

9.Genes are passed on from one generation to the next!

Use the diagram to draw a pedigree chart

10.Genes are passed on from one generation to the next!

What is your

blood type?

11.Genes are passed on from one generation to the next!

The inheritance of blood types A, B, AB and O are determined by the ABO gene.

Three different alleles for the ABO gene. Two carry instructions to make a particular type of protein called an

antigen; the other does not. One allele codes for antigen A and the other codes for antigen B. If you possess both of these alleles, then you have the instructions to

produce both antigen A and antigen B.

This is an example of co-dominant inheritance because both blood types are expressed in the heterozygote.

What is your blood type? 12.Genes are passed on from one generation to the next!Co-dominance

Heterozygote has the characteristics of both parents(e.g. human blood groups)

Calculating Co-dominant Inheritance

13.Genes are passed on from one generation to the next!

Refer to the ABO gene as I, the allele that codes for antigen A could be referred to as IA.

Antigen B could be referred to as IB. Neither antigen could be referred to as I, The ability to make antigen A or B is shown as a capital letter

because it is dominant. The inability to make either antigen is recessive and shown as a

lowercase letter.

14.Genes are passed on from one generation to the next!

Calculating Co-dominant Inheritance

Can you have a different blood type to your parents?

15.Genes are passed on from one generation to the next!

Discuss the question with a person nearby

Chromosomes can be

Autosomes or Sex Chromosomes

16.Genes are passed on from one generation to the next!

Somatic cells have 23 pairs of chromosomes, numbered 1-23 depending of size.

22 pairs of autosomes

1 pair of sex chromosomes

• Males have XY• Females have XX

Inheritance 17.Genes are passed on from one generation to the next!The passing of characteristics from one generation

to the next

Inheritance can be: Autosomal inheritance (Chromosomes that are not X or Y)

Inheritance of traits where genes are located on autosomes Sex-linked inheritance (Chromosomes that are X or Y)

Inheritance of traits where genes are located on sex chromosomes

X-Linked Inheritance (On X Chromosome) Y-Linked inheritance (On Y Chromosome)

Most examples of Sex linked inheritance (Sex-linkage) are X-linkage, since the Y chromosome is small and does not contain many genes.

Sex-linked inheritance Examples of X-linked recessive traits are:

Haemophilia some forms of Colour blindness Females need to receive two alleles for the

recessive trait, males need to receive only one. There is a greater chance of males showing these

traits than females.

Genotype for X-linked traits Heterozygous, XBXb

Homozygous, XbXb or XBXB.

18.Genes are passed on from one generation to the next!

Males, who possess only one X chromosome, are hemizygous and would have the genotypes XBY or XbY. When stating the phenotypes for X-linked traits it is important to also specify the person’s gender (e.g. colour blind male).

Can males be homozygous for an X-linked trait?

19.Genes are passed on from one generation to the next!

Discuss the question with a person nearby

X-Linked Inheritance20.Genes are passed on from one generation to the next!

Variation in a family! In each family there are similarities and also differences!

Traits can “skip” a generation if parents are carriers of a recessive allele.

There are 8 388 608 possible chromosome combinations when forming gametes during Meiosis!

Crossing over can occur between chromosomes, one chromosome swaps its genetic information with another.

21.Genes are passed on from one generation to the next!