Post on 31-Dec-2015
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INTRODUCTION TO GENETICS
Ms. Wassum
Traits
• Traits are the different forms of a characteristic that you may exhibit• Ex: Blue or Brown Eyes
• Traits are inherited from our parents
• Therefore, when we talk about genetics, we are talking about sexual reproduction
Chromosomes
• Every cell in a human body has 23 pairs of chromosomes – half from our mother, half from our father
• Genes are found on chromosomes• We have about 20,000-25,000 genes
• Each gene holds a code that tells our body to make
a certain protein• The protein that is made determines a
Specific trait. Ex: Blue eye pigment or
Brown eye pigment
Alleles
• The different forms of a gene that can exist• Ex: Curly hair gene or straight hair gene
• Dominant – ‘Strongest Allele’ – If it is present, you will have that trait. We use upper case letters for dominant alleles
• Recessive – ‘Weakest Allele’ – This won’t show up unless there are two of them. We use lower case letters for recessive alleles
Genotype
• The actual alleles you have for a trait• Ex: For eye color, you inherit B from dad and b from
Mom• Your genotype is Bb• If there is a dominant allele, the genotype is written
with the upper case first. (Never write bB)
• Your genotype is the genes you have
Genotype (Cont’d)
• If you have two copies of the same allele for a trait (BB or bb), then you are HOMOZYGOUS for that trait
• If you have two different alleles for a trait (Bb), then you are HETEROZYGOUS for that trait
Phenotype
• How the genes actually show up, or how they are expressed
• So, if your genotype is Bb,• Where B is brown• And b is blue
• The phenotype would be Brown eyes
• Phenotype is the physical appearance
Karyotype-Normal
A picture of the chromosomes found in an individual. Used to determine abnormalities.
Karyotype - Abnormal
There are three copies of chromosome 21 – there should only be two copies. This is a karyotpe of a female with Down’s Syndrome.
Quiz Time
• You inherit the gene for freckles (F) from dad, and the gene for no freckles (f) from mom
1. What would your genotype be? • Ff
2. What would your phenotype be?• You would have freckles
3. Which allele is dominant?• F (freckles)
Quiz Time
• You inherit the gene for no allergies (a) from dad, and the gene for allergies (A) from mom
1. What would your genotype be? • Aa
2. What would your phenotype be?• You would have allergies
3. Which allele is dominant?• A (allergies)