Generating New Generations

Reproduction and Growth All living things reproduce Reproduction guarantees that a species’ genes are passed on to the next generation Organisms use one of two main methods to produce offspring- asexual and sexual reproduction

Asexual Reproduction Simplest form of reproduction Involves only one parent Offspring only inherit the genes from of that parent Produce offspring that are genetically identical to the parent Examples: Animals such as corals, starfish, sponges, and certain jellyfish Many plants, fungi, bacteria, and protozoans

Types of Asexual Reproduction Budding- Offspring grows from the parent until it fully matures and breaks off (ex. corals, sponges, and sea anemones) Fission- The cell’s contents are replicated internally and then divides into two distinct entities (ex. single cell organisms like prokaryotes and some protozoa) Fragmentation- New organism forms from a piece of the original (ex. new sea star may form from an arm that breaks off)

Types of Asexual Reproduction Parthenogenesis- Female organisms produce female offspring within their bodies without being fertilized by a male (ex. some amphibians) Spores- Parent releases spores that develop into fully grown organisms when conditions are environmentally suitable (ex. some protozoans, bacteria, plants, and fungi) Vegetative- Some plants use specialized genetic features that allow them to reproduce without seeds or spores (ex. aerial stems of strawberries, bulbs of tulips, and the tubers of potatoes)

Sexual Reproduction Two parents combine their genetic material to produce a new organism Offspring are not exact copies of the parents, instead they display traits which differ from both parents Responsible for the variety of life on our planet

Sexual Reproduction Forms New Cells During fertilization an egg and a sperm cell join to form a new cell Each egg cell and sperm cell contains half of the parent’s chromosomes When fertilization occurs, a full set of chromosomes is present in the new cell Results in a combination of specific characteristics known as traits Traits are passed to an offspring by a sequence of DNA on the chromosomes known as genes Create the individual variations found in the offspring

Comparing Types of Reproduction Advantages Advantages of Asexual Reproduction Advantages of Sexual Reproduction Can produce offspring quickly- -Useful for species who’s survival strategy is to reproduce fast (ex. bacteria) Offspring have greater genetic variations- -Creates diversity Doesn’t require a mate- -Enables isolated species to create offspring 2. Promotes survival- -Offspring may inherit a gene that helps them adapt to changing environments Requires less resources- - Many sea creatures and plants create offspring by cutting off part of themselves 3. Removes “bad genes” from the population

Comparing Types of Reproduction Disadvantages Disadvantages of Asexual Reproduction Disadvantages of Sexual Reproduction Lack of diversity- -With the exception of rare mutations, offspring are identical to their parent Require a mate- -Can be a problem for organisms living in isolated or remote areas 2. Organisms are more susceptible to diseases and environmental hardships- -If one individual organism is unable to tolerate a disease or change, chances are the other identical offspring wont either Takes time and energy- -Finding a mate, courtship 3. Produces fewer offspring Can prevent “favorable genes” from being passed to an offspring

Heredity and Gregor Mendel Heredity- the passing of traits from parents to offspring Gregor Mendel- Austrian monk known as the “Father of Modern Heredity” Studied heredity by cross-pollinating pea plants, from 1856 to 1863, at the monastery where he tended the gardens Experimented with 7 characteristics of pea plants (plant height, pod shape & color, seed shape & color, and flower position & color)

Mendel’s Research Mendel formulated several ideas about heredity Through experimentation, he realized that certain patterns, in the passing of characteristics (traits), formed from the parent plants to their offspring Mendel called the information that carried the traits factors (now referred to as genes or alleles), because they determined what was expressed

Mendel’s Conclusions Mendel determined that for every trait, organisms receive one factor from their mother and one from their father Concluded that one factor could mask the expression of the other, even if both were present at the same time Coined the terms “dominant” and “recessive” in reference to certain traits Dominant factors would mask the expression of recessive factors if both were present at the same time Concluded that while only one form of a trait was visible in the offspring, the missing trait sometimes shows itself in later generations

Inheriting Traits When egg and sperm cells come together, genetic information from the parents mix Inheritance is the process by which an offspring receives genes from its parents Genes are located on chromosomes and describe the factors that control a trait Each trait is described by a pair of genes, with one gene from the mother and the other from the father

Gene Pairs Sometimes the genes in a pair are both the same, and at other times, they are different from each other An allele is a different form of the same gene One allele is inherited from each parent, their combination determines which traits the offspring will have

Dominate vs. Recessive Alleles Alleles are either dominate or recessive A dominate allele is represented with a capital letter A recessive allele is represented with a lower case letter If an offspring inherits a dominant allele from either parent, that dominant trait will always show up in the offspring Offspring must inherit a recessive allele from both parents in order for the recessive trait to show

Expressing Traits In plants, T often represents a dominate allele for tall and t a recessive allele for short Purebred- Organism has two of the same allele for a trait (TT or tt) Also referred to as being homozygous Offspring inherited the same type of allele from both parents TT (homozygous dominant) all tall offspring tt (homozygous recessive) all short offspring Hybrid- Organism has one dominant and one recessive allele for a trait (Tt) Also referred to as heterozygous Offspring inherited a different type of allele from each parent Tt all offspring will be tall

Multiple Alleles Multiple alleles- Occurs when a trait has more than 2 alleles Each parent still contributes an allele which will combine to create the trait expressed in the offspring With additional number of alleles, the number of possible outcomes increases For Example, there are three types of alleles for blood type (A, B and O) The A and B blood types are codominant and O is recessive This results in four blood types are A, B, AB, and O

Incomplete Dominance & Codominance Incomplete dominance- Occurs when an intermediate form of a dominant trait appears The offspring have a mixture of the two alleles Ex. A plant with red flowers is crossed with one with white flowers, resulting in offspring with pink flowers Codominance- Occurs when two different alleles for the same gene are expressed at the same time (neither allele acts as dominant or recessive) Ex. A plant with red flowers is crossed with one with white flowers, resulting in offspring having red flowers with white stripes

Genotypes and Phenotypes Genotype- An organisms genetic make up or combination of alleles The set of genes in an organism’s DNA which are responsible for a particular trait Ex. In plants, possible genotypes for height could be TT, Tt, or tt Phenotype- An organisms appearance or visible traits The physical expression, or characteristics, of inherited traits Ex. In plants, possible phenotypes for height could be tall or short

Probability & Heredity Probability- a number that describes how likely it is that an event will occur Laws of probability predict what is, and is not, likely to happen Every time two parents produce offspring, the probability if certain traits getting passed on is the same To determine the probability of inheriting alleles, geneticists use Punnett squares

Punnett Squares Used to determine the probability of inheriting certain alleles Prior to constructing/using a Punnett square you need to know: The traits being considered Whether the parents are purebred or hybrid Example: cross between two pea plants that are both hybrid for height (Tt)

Constructing a Punnett Square Cross between two pea plants that are both hybrid for height (Tt) Draw a square box divided into four square parts Determine the alleles of each parent, then place one set of alleles on the top of the columns of the box and the other next to the rows Do the cross by combining the letter at the top of each column with the letter of the row the box is in (Always write a dominant allele before a recessive one) Determine the likelihood of the different combinations of alleles Determine which trait is expressed for each combination of alleles

Using a Punnett Square Cross between a purebred tall pea plant with a purebred short pea plant Cross between a hybrid tall pea plant with a purebred short pea plant

Genes and the Environment A combination of inherited traits and acquired traits help many organisms survive in their environments. Inherited traits are features or characteristics that result from genes passed from parents to offspring Acquired traits are physical characteristics or behaviors that are not genetically passed down to an offspring Are the result of learned behaviors and by an organisms interactions with its environment

Environmental Influence Organisms interact with their environments on a regular basis Some of these interactions may change the way a gene is expressed (how the inherited traits appear) The environment can lead to several changes in the way genes are expressed Changes in the way certain genes behave May alter the way an organism functions, producing traits that would not normally have been expressed Theses changes may cause cancer or diseases Not all changes in genes caused by environmental factors get passed to offspring In order to pass on gene that were change by the environment, the change must occur in one of the sex cells (egg or sperm)