Inheritance & Chromosomes

Inheritance & Chromosomes http://www.erichufschmid.net/Hufschmid-14Dec2008.html

Today’s Lesson • Different Types of Inheritance • Chromosomes • Male Chromosomes • Female Chromosomes • Genetic Anomolies • Activity

Inheritance • All of the information from your DNA comes from your mother and father. • A sperm and an egg are known as haploids. They both contain 1 copy of each chromosome and therefore 1 copy of each gene. • When a sperm and an egg come together – they are called a zygote. They have 2 copies of each chromosome. • Each animal has a different number of chromosomes. Humans have 46.

Inheritance • Each copy of a gene is called an allele. • If both alleles are the same, they are said to be homozygous. • If the alleles are different, they are said to be heterozygous. • The three types of inheritance are: • Dominant • Intermediate Inheritance • Co-Dominance

Inheritance • In an allele, if the letter is a capital (R) then the trait is dominant. • In an allele, if the letter is small (r) then the trait is recessive • Each individual trait is called a genotype (ie R or r). • The overall trait is called the phenotype (ie RR, Rr or rr)

Work • We will now complete a worksheet. Keep it as it will be important for your test.

Chromosomes • Each living thing has a different number of chromosomes. • Humans have 46 chromosomes. • Dogs have 78 chromosomes • Barley has 14 chromosomes • An American Beaver has 48 chromosomes • An European Beaver has 40 chromosomes • A Kangaroo has 16 chromosomes

Male Chromosomes • It’s hard to believe it – but males are almost genetically identical to females!! • The 45th and 46th chromosome is what separates us. These chromosomes can either be X or Y. • Males have an X or Y chromosome. • This also means that males are more likely to suffer from genetic disorders found on these chromosomes (such as hemophilia)

Female Chromosomes • Unlike males, females have two X chromosomes. • The egg is always an X chromosome. This means it’s the sperm which decides the sex of the baby – not the woman!! • Having female genitals does not mean that you are a female genetically • http://www.hhmi.org/biointeractive/gendertest/gendertest.html

Genetic Anomalies • Sometimes, there are problems with the chromosomes when they are produced. Below are some examples: • XX Male Syndrome: There are male genitals, but they are sterile. They are genetically female but look male. • XXY Male Syndrome: They have male genitals and are taller than normal. Normally they have learning difficulties and other medical problems.

Genetic Anomalies • XXX Female Syndrome – The female has one extra copy of X. They normally tend to have a lower than average IQ (90 – with 100 being normal) but are fertile. The children do not inherit the traits. • X Turner Female Syndrome. One of the X chromosomes is missing. They are normally shorter than normal and infertile. Problems with intelligence are common.

Activity • Collect an A3 sheet, scissors, glue (you will need to share!!) and an A4 sheet. • Cut out all of the 46 chromosomes. Match them together looking at the patterns • Glue them down starting with the largest to the smallest pairs. Finish with the sex chromosomes. • Say if it’s a boy, girl and if there is a genetic disorder…

Inheritance & Chromosomes