Chapter 4.1, 4.2C

Make a list of the characteristics you see in the 3 children in the picture:

4.1: Parents and Offspring are Similar  Traits are either:  Inherited: traits you get from your parents (hair color, eye color, face shape, etc…)  Acquired: developed over your lifetime (learned behaviors, i.e. reading, writing, riding a bike, etc…)

Traits are Controlled by Genes  Genes: located on chromosomes and code for a particular product (trait)  You inherit genes from your parents (heredity)  Your cells contain 23 chromosome pairs (homologs) to equal your 46 chromosomes You received half of each homolog from your mother. your father.

Traits are Controlled by Genes  Each homolog contains sites where genes are located.  Though the gene may be present on both, the form of the gene may be different.  Alleles: the various forms of the same gene

Chromosome Pairs  Humans chromosomes are numbered 1- 22; the 23rd pair are the sex chromosomes  Sex chromosomes are X-chromosomes and Y-chromosomes  Female: XX  Male: XY

 female male 

Gregor Mendel made some important discoveries about heredity…  Performed an experiment with pea plants  Discovered that each plant must have two factors for each possible trait, one factor from each parent (Mendel’s “factors” are now known as genes and alleles)  Alleles interact to produce traits

Alleles Interact to Produce Traits  Phenotype: describes your physical characteristics that can be observed (eye color, hair color)  Genotype describes the actual genes that you have on your DNA; not always obvious

Alleles Interact to Produce Traits  Mendel found that we have two copies of each allele (one from mom, one from dad)  Alleles can be  Dominant  Physically expressed regardless of what other allele it is paired with  Always expressed as a capital letter (T) (Ex: tallness is the dominant trait for pea plant height)  Recessive  Physically expressed only when paired with another recessive allele  Always expressed as a lower-case letter (t) (Ex: dwarfism is the recessive trait for pea plant height)

4.2: Punnett Squares  Punnett Squares show possible outcomes for inheritance.  Mendel noticed that traits are inherited in patterns.  Punnett squares illustrate how the parents’ alleles might combine in offspring.  Each parent has two alleles for a particular gene. An offspring receives one allele from each parent. A Punnett square shows how the parents’ alleles may be passed on to potential offspring.

Punnett Squares  The letter “T”/”t” will refer to height (“T” being tall  dominant; “t” being short  recessive)

Ratios and percentages can express the probability of outcomes  Probability: the likelihood or chance of a specific outcome in relation to the total number of possible outcomes  Ratio: compares the relationship of two quantities  Percentage: a ratio that compares a number to 100

Practice…  A TT (tall) plant is crossed with a tt (short plant).  What is the ratio of tall to short offspring?  What percentage of the offspring will be tall?

 It is important to realize that Punnett squares and probability do not guarantee the outcome of a genetic cross. They indicate the probability of different outcomes. Actual experimental results may not match predicted outcomes.