LIVING THINGS INHERIT TRAITS IN PATTERNS

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 You received half of

each homolog from each homolog from

your mother. your father.

Traits are Controlled by Genes

Each homolog contains sites where genesare 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

male

female

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 ofeach 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 talldominant; “t” being shortrecessive)

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.