Inheritance

Topic 3.4

Essential idea: The inheritance of genes follows pattern.

Understandings

3.4.U1 Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed

An outline of some of the monohybrid crosses of pea plants carried out by Gregor Mendel.

Place mouse pointer on the figure to see the dominant trait in each cross.

Mendel's experiments and the dominant trait

3.4.U2 Gametes are haploid so contain only one allele of each gene

Gametes contain haploid gametes

3.4.U3 The alleles of each gene separate into different haploid daughter nuclei during meiosis

One allele per gamete

3.4.U4 Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles

Diploid zygote

3.4.U5 Dominant alleles can mask the effects of recessive alleles but co-dominant alleles have joint effects

Dominant and codominant effects

3.4.U6 Many genetic diseases in humans are due to recessive alleles of autosomal genes, although some genetic diseases are due                      to dominant or co-dominant alleles

Use the information in the figure to determine the causes of cystic fibrosis and Huntington's disease?

Place mouse pointer on the figure to view the causes.

Examples of genetic diseases

3.4.U7 Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location                      on sex chromosomes

How do the sex chromosomes control gender?

Sex chromosomes and gender determination

Difference between the X chromosome and Y chromosome in humans?

Place mouse pointer on the figure to see chromosome conclusion.

X and Y chromosome difference

3.4.U8 Many genetic diseases have been identified in humans but most are very rare

Rare genetic disease stats

3.4.U9 Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer

Mutagens genetic diseases cancer

Applications

3.4.A1 Inheritance of ABO blood groups

ABO blood groups are an example of codominance and how some genes have more than two alleles (i.e., multiple alleles). Test yourself: if a man has blood group O and a woman has blood group AB, what is the probability that their child will be blood group O? Hint use a Punnett grid to determine the genotypes and phenotypes of a monohybrid cross between the man and woman. Placing your mouse pointer on the figure below will show the answer.

abo blood groups link abo blood groups animation
ABO blood groups

3.4.A2 Red-green color blindness and hemophilia are examples of sex linked inheritance

Gender is determined by the sex chromosomes where males have an X and a Y chromosome and females have two X chromosomes. It is important to note that some genes are present on the X chromosome and absent on the shorter Y chromosome in humans. This can lead to diseases that are sex-linked where the disease is caused by a gene located on a sex chromosome (e.g., colorblindness and hemophilia). Test yourself: a woman's father has hemophilia, but her husband does not. What is the probability of the woman having a child with hemophilia? Hint use a Punnett grid to determine the genotypes and phenotypes of a monohybrid cross between the woman and her husband. Placing your mouse pointer on the figure below will show the answer.

Sex Linkage explained

3.4.A3 Inheritance of cystic fibrosis and Huntington's disease

Place mouse pointer on the figure to view monohybrid cross and explanation on how it is inherited.

Cystic Fibrosis monohybrid cross

Place mouse pointer on the figure to view monohybrid cross and explanation on how it is inherited.

Cystic Fibrosis monohybrid cross

3.4.A4 Consequences of radiation after nuclear bombing of Hiroshima an accident at Chernobyl

Consequences of radiation: Hiroshima and Chernobyl

Skills

3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses

Key Definitions

Determine the genotypes and phenotypes of the offspring of a monohybrid cross between a homozygous, dominant yellow pea plant with a homozygous, recessive green pea plant. Shown below are the steps, numbered 1 to 4, to complete this problem. Test yourself: determine the genotypes and phenotypes of a monohybrid cross between the F1 offspring (i.e., Yy x Yy). Placing your mouse pointer on the figure below will show the genotypes and phenotypes of the offspring of the F1 cross.

Monohybrid Crosses

3.4.S2 Comparison of predicted and actual outcomes of genetic crosses using real data

A cross between two yellow heterozygous pea plants

Look at the cross below and complete a Punnett grid for the predicted phenotypic ratio.

Place mouse pointer on the figure to view the Punnett grid.

Predicted outcome heterozygous yellow seed cross

Does the data fit the predicted phenotypic ratio?

A chi-squared test is performed to answer the question.

Click on Go to Chi-squared Test to see how to compare predicted and actual outcomes in a monohybrid cross

Go to Chi-squared Test

3.4.S3 Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases

Pedigree Key to Symbols

Use the pedigree symbol below to help deduce the genotypes and phenotypes of individuals in pedigree charts. For dominant and recessive alleles, upper-case and lower-case letters, respectively, should be used. Letters representing the alleles should be chosen to avoid confusion with upper and lowercase. For codominance, the main letter should refer to the gene and the suffix to the allele, both uppercase. For example, red and white codominant flower colors should be represented as CR and CW, respectively. For sickle cell anemia, HbA is normal and HbS is sickle cell.

pedigree link pedigree animation
Pedigree Key to Symbols
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